BGP Troubleshooting Guide
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- Chrystal Fisher
- 7 years ago
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1 BGP Troubleshooting Guide Abstract The main purpose of this guide is to illustrate various issues encountered while configuring BGP on HP routers. This troubleshooting guide discusses ways of analyzing a problem and the corrective measures to resolve the issue for both, ProVision and Comware. This guide assumes that readers are familiar with the OSI layer and IP routing protocols. Part number:
2 Copyright 2012 Hewlett-Packard Development Company, L.P. No part of this documentation may be reproduced or transmitted in any form or by any means without prior written consent of Hewlett-Packard Development Company, L.P. The information contained herein is subject to change without notice. HEWLETT-PACKARD COMPANY MAKES NO WARRANTY OF ANY KIND WITH REGARD TO THIS MATERIAL, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. Hewlett-Packard shall not be liable for errors contained herein or for incidental or consequential damages in connection with the furnishing, performance, or use of this material. The only warranties for HP products and services are set forth in the express warranty statements accompanying such products and services. Nothing herein should be construed as constituting an additional warranty. HP shall not be liable for technical or editorial errors or omissions contained herein.
3 Contents Contents 1 BGP Neighbor Relation Establishment 3 (ProVision) no BGP packets are being sent 3 Troubleshooting 3 Solution 4 Verification 4 Incorrect IP address configured on the interface 5 Troubleshooting 5 Solution 8 Verification 8 Incorrect neighbor IP configured under peer command 9 Troubleshooting 9 Solution 10 Verification 11 Incorrect AS number included under peer command 11 Troubleshooting 12 Solution 13 Verification 13 Loopback IP not configured for indirectly connected routers 14 Troubleshooting 14 Solution 17 Verification 17 Missing Command connect-interface or update-source 18 Troubleshooting 18 Solution 20 Verification 20 Missing Command ebgp-max-hop or ebgp-multihop 21 Troubleshooting 22 Solution 22 Verification 22 Connect-interface or update-source configured for directly connected peers 23 Troubleshooting 23 Solution 24 Verification 25 No route to reach loopback interface 25 Troubleshooting 26 Solution 29 Verification 29 Ignore or shutdown command configured on BGP peer 30 Troubleshooting 30 Solution 32 Verification 32 ACL Blocking the TCP/BGP Packets 32 Troubleshooting 33 Solution 36 1
4 Verification 36 Same Router-id configured on peers (Comware Only) 37 Troubleshooting 37 Solution 38 Verification 38 2 BGP Routing Issues 39 BGP router not installing the routes in routing table 39 Network command is not announcing the configured route 39 Next-hop-local/next-hop-self command is missing 44 Troubleshooting 45 Solution 46 Verification 47 BGP router not advertising the routes 48 Router is not receiving External-AS routes or routes that are more than one hop away. 48 Problem 49 Troubleshooting 49 Solution 52 Verification 52 3 BGP Confederation issues (Comware Only) 54 BGP Confederation peer relation not establishing: Incorrect peer IP configured 54 Problem 54 Troubleshooting 54 Solution 55 Verification 55 Incorrect confederation peer-as configured 56 Troubleshooting 56 Solution 57 Verification 57 Missing confederation peer-as <AS number> command 57 Troubleshooting 58 Solution 59 Verification 59 4 BGP Route Aggregation issue 60 Router receiving both detailed routes as well as summary route (Comware only) 60 Problem 60 Troubleshooting 60 Solution 61 A manually configured summary route is not being advertised (ProVision only) 63 Problem 63 Troubleshooting 63 Solution 64 Verification 65 2
5 1 BGP Neighbor Relation Establishment Below listed are the common problems found in the BGP Neighbor relation establishment: (ProVision) no BGP packets are being sent Incorrect IP address configured on the interface Incorrect Neighbor IP configured under peer command Incorrect AS-number included under peer command Loopback ip not configured for indirectly connected routers Missing Command peer x.x.x.x connect-interface Missing Command peer x.x.x.x e-bgp maxhop <hops> Undesirable configuration of peer x.x.x.x connect-interface command for directly connected routers No route to reach loopback interface peer x.x.x.x ignore command configured under BGP configuration ACL blocking TCP/BGP packets Duplicate router-id (ProVision) no BGP packets are being sent BGP appears to be configured correctly however neither router is sending any BGP packets, and BGP peering relationships are not being established. Troubleshooting Use the show ip bgp summary command to determine if packets are being sent. The State of idle indicates no packets are being sent. RT1(bgp)# show ip bgp summary Peer Information Remote Address Remote-AS Local-AS State Admin Status Idle Start To determine the actual status of the BGP protocol, use the show ip bgp general command. RT1# show ip bgp general BGP Configuration Information Enable : No Local AS : 1 3
6 Solution Local Distance : 200 Local Identifier : Default Metric : Maximum Prefix : Always Compare MED : No Cluster-ID : Miss MED As Worst : No Compare Router ID : No Ignore AS-Path Length : No Open On Accept : No Compare Origin Id : No Allow-AS in : 0 External Distance : 20 Internal Distance : 200 Log Neighbor Changes : No C-to-C Reflection : Yes Log Prefix List : Hold Time : 180 Keep Alive : 60 Restart Time : 120 Stalepath Time : 360 Non Stop Forwarding : Disabled On ProVision platforms, the routing protocol must be explicitly enabled. The default status is disabled. The BGP routing protocol must be manually enabled inside the BGP context. RT1(config)# router bgp 1 RT1(bgp)# enable RT1(bgp)# show ip bgp general BGP Configuration Information Verification Enable : Yes Local AS : 1 Local Distance : 200 Local Identifier : Default Metric : Maximum Prefix : Always Compare MED : No Cluster-ID : Miss MED As Worst : No Compare Router ID : No Ignore AS-Path Length : No Open On Accept : No Compare Origin Id : No Allow-AS in : 0 External Distance : 20 Internal Distance : 200 Log Neighbor Changes : No C-to-C Reflection : Yes Log Prefix List : Hold Time : 180 Keep Alive : 60 Restart Time : 120 Stalepath Time : 360 Non Stop Forwarding : Disabled Use the show ip bgp summary command to verify the neighbor relationship. R2(vlan-1)# show ip bgp summary Peer Information Remote Address Remote-AS Local-AS State Admin Status
7 Established Start Incorrect IP address configured on the interface An example of an incorrect IP address configured on the interface is shown in Figure 1 and Figure 2. Figure 1 Incorrect IP address Figure 2 Incorrect IP address R1 is trying to establish a neighbor relationship with R2. R1 and R2 are directly connected routers belonging to different AS. Troubleshooting Use the display bgp peer or show ip bgp summary command to determine the BGP peer status. <R1>display bgp peer BGP local router ID : Local AS number : 6500 Total number of peers : 1 Peers in established state : 0 5
8 Peer AS MsgRcvd MsgSent OutQ PrefRcv Up/Down State :03:39 Active R1(config)# show ip bgp summary Peer Information Remote Address Remote-AS Local-AS State Admin Status Connect Start Check the ping reply. <R1>ping PING : 56 data bytes, press CTRL_C to break Request time out Request time out Request time out Request time out Request time out ping statistics packet(s) transmitted 0 packet(s) received % packet loss R1(config)# ping Request timed out. R1 is not able to ping R2 s interface ip. Check the interface status at both ends. Router R1 <R1>display int s 5/7 Serial5/7 current state: UP Line protocol current state: UP Description: Serial5/7 Interface 6
9 The Maximum Transmit Unit is 1500, Hold timer is 10(sec) Internet Address is /24 Primary Link layer protocol is PPP R1(config)# show ip Internet (IP) Service IP Routing : Enabled Default TTL : 64 Arp Age : 20 Domain Suffix : DNS server : Proxy ARP VLAN IP Config IP Address Subnet Mask Std Local DEFAULT_VLAN Manual No No Router R2 [R2]display int s 5/3 Serial5/3 current state: UP Line protocol current state: UP Description: Serial5/3 Interface The Maximum Transmit Unit is 1500, Hold timer is 10(sec) Internet Address is /24 Primary Link layer protocol is PPP R2(bgp)# show ip Internet (IP) Service IP Routing : Enabled Default TTL : 64 Arp Age : 20 Domain Suffix : DNS server : Proxy ARP VLAN IP Config IP Address Subnet Mask Std Local 7
10 DEFAULT_VLAN Manual No No Solution The IP address configured on R2 is not correct. Configure router R2 with correct Interface IP. [R2]int s 5/3 [R2-Serial5/3]ip add R2(vlan-1)# no ip address R2(vlan-1)# ip address /24 Verification Use the display bgp peer or show ip bgp summary command to verify the neighbor relationship. [R2]disp bgp peer BGP local router ID : Local AS number : 777 Total number of peers : 1 Peers in established state : 0 Peer AS MsgRcvd MsgSent OutQ PrefRcv Up/Down State :11:01 Established R2(vlan-1)# show ip bgp summary Peer Information Remote Address Remote-AS Local-AS State Admin Status Established Start 8
![[R2]disp bgp peer BGP local router ID : 2.2.2.2 Local AS number : 777 Total number of peers : 1](/docs-images/44/23195106/images/page_10.jpg "Peers in established state : 0 Peer AS MsgRcvd MsgSent OutQ PrefRcv Up/Down State 20.1.")
11 Incorrect neighbor IP configured under peer command An example of an incorrect neighbor IP address configured under peer command is shown in Figure 3. Figure 3 Incorrect neighbor IP address configured under peer command Troubleshooting Use the display bgp peer or show ip bgp summary command to verify the peer status. [R1]disp bgp peer BGP local router ID : Local AS number : 6500 Total number of peers : 1 Peers in established state : 0 Peer AS MsgRcvd MsgSent OutQ PrefRcv Up/Down State :00:22 Active R1(config)# show ip bgp summary Peer Information Remote Address Remote-AS Local-AS State Admin Status Active Start BGP peer status is stuck in Active. Check the BGP configuration on both routers. 9
![[R1]disp bgp peer BGP local router ID : 1.1.1.1 Local AS number : 6500 Total number of peers : 1 Peers in established state : 0 Peer AS MsgRcvd MsgSent OutQ PrefRcv Up/Down State 20.1.1.2 777 0 0 0 0](/docs-images/44/23195106/images/page_11.jpg "00:00:22 Active R1(config)# show ip bgp summary Peer Information Remote Address Remote-AS Local-AS State Admin Status --------------- --------- -------- ------------- ------------ 20.1.1.2 777 6500 Active Start BGP peer status is stuck in Active.")
12 Router R1 [R1]disp current-configuration begin bgp bgp 6500 undo synchronization timer keepalive 6 hold 18 peer as-number 777 R1(config)# show run router bgp 6500 enable neighbor remote-as 777 exit Router R2 [R2]disp current-configuration begin bgp bgp 777 undo synchronization timer keepalive 5 hold 30 peer as-number 6500 Solution R2(config)# show run router bgp 777 enable neighbor remote-as 6500 exit The peer command is followed by the incorrect IP address on R2. Correct the peer command configured on R2. 10
13 [R2]bgp 777 [R2-bgp]undo peer [R2-bgp]peer as-number 6500 R2(bgp)# router bgp 777 R2(bgp)# no neighbor R2(bgp)# neighbor remote-as 6500 Verification Verify the BGP peer relationship status. [R2]disp bgp peer BGP local router ID : Local AS number : 777 Total number of peers : 1 Peers in established state : 1 Peer AS MsgRcvd MsgSent OutQ PrefRcv Up/Down State :00:10 Established R1(config)# show ip bgp summary Peer Information Remote Address Remote-AS Local-AS State Admin Status Established Start Incorrect AS number included under peer command An example of an incorrect AS number included under peer command is shown in Figure 4. 11
14 Figure 4 Incorrect AS number included under peer command Troubleshooting Verify the BGP peer status using the command display bgp peer or show ip bgp summary. <R1>disp bgp peer BGP local router ID : Local AS number : 6500 Total number of peers : 1 Peers in established state : 0 Peer AS MsgRcvd MsgSent OutQ PrefRcv Up/Down State :00:31 Active R1(config)# show ip bgp summary Peer Information Remote Address Remote-AS Local-AS State Admin Status Active Start Check the BGP configurations at both ends. Router R1 [R1]disp current-configuration begin bgp bgp 6500 undo synchronization timer keepalive 6 hold 18 peer as-number
15 R1(config)# show run router bgp 6500 enable neighbor remote-as 777 exit Router R2 [R2]disp current-configuration begin bgp bgp 777 undo synchronization timer keepalive 5 hold 30 peer as-number 6502 Solution R2(config)# show run router bgp 777 enable neighbor remote-as 6502 exit The as-number configured under BGP peer command on R2 is incorrect. Configure the Neighbor IP under correct AS [R2]bgp 777 [R2-bgp]undo peer [R2-bgp]peer as-number 6500 R2(bgp)# router bgp 777 R2(bgp)# no neighbor R2(bgp)# neighbor remote-as 6500 Verification 13
![Configure the Neighbor IP under correct AS [R2]bgp 777 [R2-bgp]undo peer 20.1.1.1 [R2-bgp]peer 20.1.1.1 as-number 6500 R2(bgp)# router bgp 777 R2(bgp)# no neighbor 20.](/docs-images/44/23195106/images/page_15.jpg "1.1.1 R2(bgp)# neighbor 20.1.1.1 remote-as 6500 Verification 13")
16 Use display bgp peer or show ip bgp summary command to verify the BGP peer status. [R2]disp bgp peer BGP local router ID : Local AS number : 777 Total number of peers : 1 Peers in established state : 1 Peer AS MsgRcvd MsgSent OutQ PrefRcv Up/Down State :00:23 Established R1(config)# show ip bgp summary Peer Information Remote Address Remote-AS Local-AS State Admin Status Established Start Loopback IP not configured for indirectly connected routers An example of a loopback IP not configured for indirectly connected routers is shown in Figure 5. Figure 5 Loopback IP not configured for indirectly connected routers Troubleshooting Verify the BGP peer status using the command display bgp peer or show ip bgp summary. 14
17 [R1]disp bgp peer BGP local router ID : Local AS number : 6500 Total number of peers : 1 Peers in established state : 0 Peer AS MsgRcvd MsgSent OutQ PrefRcv Up/Down State :00:05 Idle R1(lo-0)# show ip bgp summary Peer Information Remote Address Remote-AS Local-AS State Admin Status Idle Start [R2]disp bgp peer BGP local router ID : Local AS number : 777 Total number of peers : 1 Peers in established state : 0 Peer AS MsgRcvd MsgSent OutQ PrefRcv Up/Down State :01:42 Active R2(bgp)# show ip bgp summary Peer Information Remote Address Remote-AS Local-AS State Admin Status Connect Start Ping the loopback IPs to verify connectivity. Router R1 [R1]ping PING : 56 data bytes, press CTRL_C to break Reply from : bytes=56 Sequence=0 ttl=255 time=25 ms Reply from : bytes=56 Sequence=1 ttl=255 time=26 ms Reply from : bytes=56 Sequence=2 ttl=255 time=26 ms 15
18 Reply from : bytes=56 Sequence=3 ttl=255 time=26 ms Reply from : bytes=56 Sequence=4 ttl=255 time=25 ms ping statistics packet(s) transmitted 5 packet(s) received 0.00% packet loss round-trip min/avg/max = 25/25/26 ms R1(lo-0)# ping is alive, time = 2 ms <R2>ping PING : 56 data bytes, press CTRL_C to break Request time out Request time out Request time out Request time out Request time out ping statistics packet(s) transmitted 0 packet(s) received % packet loss R2(bgp)# ping Request timed out. Check the loopback interface of R1 [R1]disp int lo 0 LoopBack0 current state: UP Line protocol current state: UP (spoofing) Description: LoopBack0 Interface The Maximum Transmit Unit is 1536 Internet protocol processing : disabled 16
19 R1(lo-0)# show ip Internet (IP) Service IP Routing : Enabled Default TTL : 64 Arp Age : 20 Domain Suffix : DNS server : Proxy ARP VLAN IP Config IP Address Subnet Mask Std Local DEFAULT_VLAN Manual No No The loopback interface is up but no ip has been configured. Solution NOTE: ProVision switch shows an absence of configuration on lo0. Configure the loopback interface of R1. [R1]int lo 0 [R1-LoopBack0]ip add R1(config)# int loop 0 R1(lo-0)# ip address Verification Verify the BGP peer relationship status using the command display bgp peer. [R1]disp bgp peer BGP local router ID : Local AS number :
![Solution NOTE: ProVision switch shows an absence of configuration on lo0. Configure the loopback interface of R1. [R1]int lo 0 [R1-LoopBack0]ip add 1.1.1.1 32 R1(config)# int loop 0 R1(lo-0)# ip address 1.](/docs-images/44/23195106/images/page_19.jpg "1.1.1 Verification Verify the BGP peer relationship status using the command display bgp peer. [R1]disp bgp peer BGP local router ID : 1.1.1.1 Local AS number : 6500 17")
20 Total number of peers : 1 Peers in established state : 1 Peer AS MsgRcvd MsgSent OutQ PrefRcv Up/Down State :00:26 Established R1(lo-0)# show ip bgp summary Peer Information Remote Address Remote-AS Local-AS State Admin Status Established Start Missing Command connect-interface or updatesource An example of a missing command is shown in Figure 6. Figure 6 Missing command Troubleshooting Verify the BGP peer status using the command display bgp peer or show ip bgp summary. [R2]disp bgp peer BGP local router ID : Local AS number : 777 Total number of peers : 1 Peers in established state : 0 18
21 Peer AS MsgRcvd MsgSent OutQ PrefRcv Up/Down State :00:11 Idle R2(bgp)# show ip bgp summ Peer Information Remote Address Remote-AS Local-AS State Admin Status Active Start Verify the BGP configurations on both routers. Router R1 [R1]disp current-configuration begin bgp bgp 6500 router-id undo synchronization peer as-number 777 : R1(lo-0)# show run router bgp 6500 enable neighbor remote-as 777 exit Router R2 <R2>disp current-configuration begin bgp bgp 777 router-id undo synchronization peer as-number
22 : R2(bgp)# show run router bgp 777 enable neighbor remote-as 6500 exit connect-interface or update-source command is missing from the BGP configurations on both routers. This command is mandatory when peering on loopback interfaces. This command forces BGP to use the loopback interface as the source address for outgoing BGP packets, rather than the native IP address of the outgoing interface. Solution Include the command under the BGP configuration. Router R1 [R1]bgp 6500 [R1-bgp]peer connect-interface lo 0 R1(bgp)# router bgp 6500 R1(bgp)# neighbor update-source Router R2 [R2]bgp 777 [R2-bgp]peer connect-interface lo 0 R2(config)# router bgp 777 R2(bgp)# neighbor update-source Verification Verify the BGP peer relationship status using the command display bgp peer or show ip bgp summary. 20
23 [R2]disp bgp peer BGP local router ID : Local AS number : 777 Total number of peers : 1 Peers in established state : 1 Peer AS MsgRcvd MsgSent OutQ PrefRcv Up/Down State :00:12 Established R2(bgp)# show ip bgp summary Peer Information Remote Address Remote-AS Local-AS State Admin Status Established Start NOTE: The "ebgp-max-hop" or ebgp-multihop command is not required when peering with the loopback ip address of a directly connected router. Missing Command ebgp-max-hop or ebgpmultihop An example of a missing command ebgp-max-hop or edgp-multihop is shown in Figure 7. Figure 7 Missing command ebgp-max-hop or edgp-multihop 21
24 Troubleshooting Two indirectly connected EBGP neighbors do not form neighbor relation if the command peer x.x.x.x e-bgp maxhop <hops> or neighbor x.x.x.x ebgp-multihop <hops> is missing from the BGP configuration. Solution This command specifies the number of hops required to reach the neighbor router. If the number of hops configured in the BGP configuration is less than the actual hops needed to reach the router, a neighbor relationship cannot be established. Configure the command peer x.x.x.x ebgp-max-hop <hops> or neighbor x.x.x.x ebgp-multihop <number> with the proper hop counts. Verification Verify the BGP peer relationship status using the command display bgp peer or show ip bgp summary. [R2]disp bgp peer BGP local router ID : Local AS number : 777 Total number of peers : 1 Peers in established state : 1 Peer AS MsgRcvd MsgSent OutQ PrefRcv Up/Down State :00:12 Established R2(bgp)# show ip bgp summary Peer Information Remote Address Remote-AS Local-AS State Admin Status Established Start 22
25 Connect-interface or update-source configured for directly connected peers An example of a connect-interface or update-source configured for directly connected peers is shown in Figure 8. Figure 8 Connect-interface or update-source configured for directly connected peers Troubleshooting Verify the BGP peer status using the command display bgp peer. [R2]display bgp peer BGP local router ID : Local AS number : 6501 Total number of peers : 1 Peers in established state : 0 Peer AS MsgRcvd MsgSent OutQ PrefRcv Up/Down State :00:18 Active R2(lo-0)# show ip bgp summary Peer Information Remote Address Remote-AS Local-AS State Admin Status Connect Start Verify the BGP configurations on both routers. Router R1 23
26 [R1]disp current-configuration begin bgp bgp 6500 peer as-number 6501 R1(bgp)# show run router bgp 6500 enable neighbor remote-as 6501 exit Router R2 [R2]disp current-configuration begin bgp bgp 6501 peer as-number 6500 peer connect-interface LoopBack0 : R2(lo-0)# show run router bgp 6501 enable neighbor remote-as 6500 neighbor update-source exit Solution Remove the incorrect command from the BGP configuration on R2. [R2]bgp 6501 [R2-bgp]undo peer connect-interface R2(lo-0)# router bgp 6501 R2(bgp)# no neighbor update-source 24
27 Verification Verify the BGP peer relationship status using the command display bgp peer or show ip bgp summary. : [R2]disp bgp peer BGP local router ID : Local AS number : 6501 Total number of peers : 1 Peers in established state : 0 Peer AS MsgRcvd MsgSent OutQ PrefRcv Up/Down State :00:18 Established R2(bgp)# show ip bgp summary Peer Information Remote Address Remote-AS Local-AS State Admin Status Established Start No route to reach loopback interface An example of no route to reach loopback interface is shown in Figure 9 and Figure 10. Figure 9 No route to reach loopback interface 25
28 Figure 10 No route to reach loopback interface Troubleshooting Verify the BGP peer status using the command display bgp peer or show ip bgp summary. [R1]disp bgp peer BGP local router ID : Local AS number : 6500 Total number of peers : 1 Peers in established state : 0 Peer AS MsgRcvd MsgSent OutQ PrefRcv Up/Down State :00:25 Active R1(bgp)# show ip bgp summary Peer Information Remote Address Remote-AS Local-AS State Admin Status Connect Start Ping the loopback IPs to verify the connectivity. Router R1 R1]ping PING : 56 data bytes, press CTRL_C to break 26
29 Reply from : bytes=56 Sequence=0 ttl=255 time=25 ms Reply from : bytes=56 Sequence=1 ttl=255 time=26 ms Reply from : bytes=56 Sequence=2 ttl=255 time=26 ms Reply from : bytes=56 Sequence=3 ttl=255 time=26 ms Reply from : bytes=56 Sequence=4 ttl=255 time=25 ms ping statistics packet(s) transmitted 5 packet(s) received 0.00% packet loss round-trip min/avg/max = 25/25/26 ms : R1(bgp)# ping is alive, time = 2 ms Router R2 [R2]ping PING : 56 data bytes, press CTRL_C to break Request time out Request time out Request time out Request time out Request time out ping statistics packet(s) transmitted 0 packet(s) received % packet loss R2(config)# ping The destination address is unreachable. Check the routing table of R1 and R2. Router R1 [R1]disp ip routing-table Routing Tables: Public Destinations : 9 Routes : 9 27
30 Destination/Mask Proto Pre Cost NextHop Interface /32 Direct InLoop /32 Static S5/ /24 Direct S5/ /32 Direct InLoop /32 Direct S5/ /8 Direct InLoop /32 Direct InLoop /24 Direct GE0/ /32 Direct InLoop0 R1(bgp)# show ip route IP Route Entries Destination Gateway VLAN Type Sub-Type Metric Dist /32 lo0 connected / static /24 DEFAULT_VLAN 1 connected /8 reject static /32 lo0 connected /24 VLAN2 2 connected / bgp R1 has a static route to R2 s loopback ip. Router R2 [R2]disp ip routing-table Routing Tables: Public Destinations : 6 Routes : 6 Destination/Mask Proto Pre Cost NextHop Interface /32 Direct InLoop /24 Direct S5/ /32 Direct S5/ /32 Direct InLoop /8 Direct InLoop /32 Direct InLoop0 28
31 R2(config)# show ip route IP Route Entries Destination Gateway VLAN Type Sub-Type Metric Dist /32 lo0 connected /24 VLAN2 2 connected /24 DEFAULT_VLAN 1 connected /8 reject static /32 lo0 connected 1 0 R2 does not have a route to R1 s loopback interface. Solution Configure a static route on R2 to confirm the connectivity to the loopback network on R1. [R2]ip route-static R2(config)# ip route Verification Verify the BGP peer relationship status using the command display bgp peer. [R2]disp bgp peer BGP local router ID : Local AS number : 777 Total number of peers : 1 Peers in established state : 1 Peer AS MsgRcvd MsgSent OutQ PrefRcv Up/Down State :00:08 Established R2(config)# show ip bgp summary Peer Information Remote Address Remote-AS Local-AS State Admin Status Established Start Established Start 29
32 Ignore or shutdown command configured on BGP peer An example of ignore or shutdown command configured on BGP peer is shown in Figure 11. Figure 11 Ignore or shutdown command configured on BGP peer Troubleshooting Verify the BGP peer status using the command display bgp peer or show ip bgp summary. Router R2 [R2]disp bgp peer BGP local router ID : Local AS number : 777 Total number of peers : 2 Peers in established state : 1 Peer AS MsgRcvd MsgSent OutQ PrefRcv Up/Down State :01:54 Idle(Admin) :47:32 Established R2(bgp)# show ip bgp summary Peer Information Remote Address Remote-AS Local-AS State Admin Status Idle Stop 30
33 Router R1 [R1]disp bgp peer BGP local router ID : Local AS number : 6500 Total number of peers : 1 Peers in established state : 0 Peer AS MsgRcvd MsgSent OutQ PrefRcv Up/Down State :02:46 Active R1(bgp)# show ip bgp summary Peer Information Remote Address Remote-AS Local-AS State Admin Status Active Start The display bgp peer or show ip bgp summary command on R2 shows that the peer status is idle(admin) or Stop. This means that peer relationship is administratively down. The ignore or shutdown command is a way to suspend BGP peering without deleting commands from the configuration. Check the BGP configuration on R2. [R2]disp current-configuration begin bgp bgp 777 network undo synchronization peer as-number 6500 peer as-number 777 peer ignore peer connect-interface LoopBack0 R2(bgp)# show run router bgp 777 enable network network neighbor remote-as
34 Solution neighbor shutdown neighbor update-source neighbor remote-as 777 neighbor next-hop-self exit Undo ignore or shutdown command. [R2]bgp 777 [R2-bgp]undo peer ignore Verification Verify the BGP peer relationship status using the command display bgp peer. [R2]disp bgp peer BGP local router ID : Local AS number : 777 Total number of peers : 2 Peers in established state : 2 Peer AS MsgRcvd MsgSent OutQ PrefRcv Up/Down State :00:19 Established :47:32 Established R2(bgp)# show ip bgp summary Peer Information Remote Address Remote-AS Local-AS State Admin Status Established Start ACL Blocking the TCP/BGP Packets An example of ACL blocking the TCP/BGP packets is shown in Figure
35 Figure 12 ACL blocking the TCP/BGP packets Troubleshooting Use display bgp peer or show ip bgp summary command to determine the BGP peer status. <R3>display bgp peer BGP local router ID : Local AS number : 6502 Total number of peers : 1 Peers in established state : 1 Peer AS MsgRcvd MsgSent OutQ PrefRcv Up/Down State :01:30 Active R3(bgp)# show ip bgp summary Peer Information Remote Address Remote-AS Local-AS State Admin Status Active Start Verify the BGP configuration on both routers. 33
36 Router R3 <R3>disp current-configuration begin bgp bgp 6502 undo synchronization peer as-number 6501 R3(bgp)# show run router bgp 6502 enable neighbor remote-as 6501 exit Router R2 <R2>disp current-configuration begin bgp bgp 6501 undo synchronization peer as-number 6502 R2(bgp)# show run router bgp 6501 enable neighbor remote-as 6500 neighbor remote-as 6502 exit step1: Check the ip address and subnet mask of the respective interfaces at both ends. step2: Check the ping reply to the respective interfaces. step3: Check the configuration on the interface. Is there any ACL configured? Router R2 <R2>disp current-configuration begin interface : : : 34
37 interface GigabitEthernet0/1 port link-mode route ip address vlan 2 name "VLAN2" untagged 2 ip address exit Router R3 <R3>disp current-configuration begin interface : : : interface GigabitEthernet0/1 port link-mode route firewall packet-filter 3000 outbound ip address vlan 2 name "VLAN2" untagged 2 ip address ip access-group "100" out exit Check the ACL configured on interface Gi 0/1 or Vlan 2 of R3. [R3]disp acl all Advanced ACL 3000, named -none-, 1 rule, ACL's step is 5 rule 10 deny tcp (70 time(s) matched) R3(bgp)# show access-list
38 Access Control Lists Name: 100 Type: Extended Applied: Yes SEQ Entry Action: deny Src IP: Mask: Port(s): Dst IP: Mask: Port(s): Proto : TCP TOS : - Precedence: - Solution The ACL on the R3-interface is blocking all the TCP packets preventing establishment of a neighbor relationship. Modify the ACL rule to allow TCP packets [R3]acl number 3000 [R3-acl-adv-3000]rule 5 permit tcp destination R3(config)# ip access-list extended 100 R3(config-ext-nacl)# 5 permit tcp any host Verification Use the display bgp peer or show ip bgp summary command to verify that neighbor relationship has been established. <R3>disp bgp peer BGP local router ID : Local AS number : 6502 Total number of peers : 1 Peers in established state : 1 Peer AS MsgRcvd MsgSent OutQ PrefRcv Up/Down State :01:47 Established R3(config-ext-nacl)# show ip bgp summary 36
39 Peer Information Remote Address Remote-AS Local-AS State Admin Status Established Start Same Router-id configured on peers (Comware Only) An example of same router-id configured on peers is shown in Figure 13. Figure 13 same router-id configured on peers Troubleshooting Use display bgp peer command to determine the BGP peer status. Router R1: <R1>disp bgp peer BGP local router ID : Local AS number : 6500 Total number of peers : 1 Peers in established state : 0 Peer AS MsgRcvd MsgSent OutQ PrefRcv Up/Down State :00:45 Active Router R2 <R2>disp bgp peer BGP local router ID : Local AS number : 777 Total number of peers : 1 Peers in established state : 0 37
40 Peer AS MsgRcvd MsgSent OutQ PrefRcv Up/Down State :00:05 Idle Check the BGP configuration. Router R1 [R1]disp current-configuration begin bgp bgp 6500 router-id undo synchronization timer keepalive 6 hold 18 peer as-number 777 Router R2 Solution [R2]disp current-configuration begin bgp bgp 777 router-id undo synchronization timer keepalive 5 hold 30 peer as-number 6500 Correct the router-id on R2 [R2]bgp 777 [R2-bgp]router-id Verification Verify the BGP peer relationship status using the command display bgp peer. [R2]disp bgp peer BGP local router ID : Local AS number : 777 Total number of peers : Peers in established state : 1 Peer AS MsgRcvd MsgSent OutQ PrefRcv Up/Down State :00:13 Established NOTE: ProVision devices allow establishment of a peer relationship when the router-ids are the same. Two ProVision devices can form a peer relationship with each other, where a Comware and ProVision device can not form a peer relationship, since the Comware device terminates the connection. 38
41 2 BGP Routing Issues BGP Routing issues can be divided into two categories: BGP router not installing the routes in routing table BGP router not advertising the routes BGP router not installing the routes in routing table Below listed are some of the reasons: network command is not announcing the configured route Next-hop-local/next-hop-self command is missing Network command is not announcing the configured route An example of network command is not announcing the configured route is shown in Figure 14. Figure 14 Network command is not announcing the configured route Problem R3 is not receiving the routes from R2 and vice versa <R3>ping
42 PING : 56 data bytes, press CTRL_C to break Request time out Request time out Request time out Request time out Request time out ping statistics packet(s) transmitted 0 packet(s) received % packet loss R3(bgp)# ping The destination address is unreachable. Ping command executed from R3 to R2 is unsuccessful. Troubleshooting Check the routing table of R3. [R3]display ip routing-table Routing Tables: Public Destinations : 7 Routes : 7 Destination/Mask Proto Pre Cost NextHop Interface /8 Direct InLoop /32 Direct InLoop /24 Direct GE0/ /32 Direct InLoop0 R3(bgp)# show ip route IP Route Entries Destination Gateway VLAN Type Sub-Type Metric Dist /24 VLAN2 2 connected /8 reject static /32 lo0 connected /24 VLAN2 2 connected
43 The routing table of R3 does not contain the routes to the network /24. Check the BGP routing table to verify the same. [R3]display bgp routing-table Total Number of Routes: 3 BGP Local router ID is Status codes: * - valid, > - best, d - damped, h - history, i - internal, s - suppressed, S - Stale Origin : i - IGP, e - EGP,? - incomplete Network NextHop MED LocPrf PrefVal Path/Ogn *> / i * i *> i R3(bgp)# show ip bgp Local AS : 6500 Local Router-id : BGP Table Version : 5 Status codes: * - valid, > - best, i - internal, e - external, s - stale Origin codes: i - IGP, e - EGP,? - incomplete Network Nexthop Metric LocalPref Weight AsPath i / i Check the ip routing table of R1. [R1]display ip routing-table Routing Tables: Public Destinations : 8 Routes : 8 Destination/Mask Proto Pre Cost NextHop Interface /32 Direct InLoop /24 BGP GE0/ /8 Direct InLoop /32 Direct InLoop /24 Direct GE0/ /32 Direct InLoop /24 Direct GE0/ /32 Direct InLoop0 41
44 R1(bgp)# show ip route IP Route Entries Destination Gateway VLAN Type Sub-Type Metric Dist /32 lo0 connected /8 reject static /32 lo0 connected /24 DEFAULT_VLAN 1 connected /24 VLAN2 2 connected 1 0 The IP routing table of R1 shows an entry for /24 network. R1 is directly connected to that network, hence IP routing table entry has an entry for direct route. Since ibgp is being used as the internal routing protocol among the routers in AS 6500, the directly connected networks must be advertised using BGP. Based on the information above, it appears that R1 is not advertising the network /24 via BGP. Check whether the BGP network advertised using network is the correct network. [R1]display bgp network BGP Local Router ID is Local AS Number is Network Mask Route-policy Short-cut R1(bgp)# show run router bgp 6500 enable network neighbor remote-as 6500 neighbor remote-as 6500 exit The output above shows that the network configured for advertising is /16. Unlike OSPF, BGP advertises a route only if the network command also has a matching route that has been installed in the global IP routing table. 42
45 In the above scenario, network command is followed by /16 subnet address. Though /16 is a supernet address and would include subnet under it, this command does not advertise the /24 network. There is no route in the global routing table that is an exact match for /24. This rule prevents advertising of a BGP route if the router is not actually able to route the packet for that specific route. Solution Remove the previously configured network command and configure the correct network command with the correct subnet mask under R1 [R1]bgp 6500 [R1-bgp]undo network [R1-bgp]network [R1-bgp]network R1(bgp)# router bgp 6500 R1(bgp)# no network R1(bgp)# network R1(bgp)# network Verification Since routes for /24 and /24 exist in the routing table of R1 as directly connected routes, R1 begins advertising those routes to both of its peers. Verify the BGP routing table of R1. [R1]display bgp routing-table Total Number of Routes: 5 BGP Local router ID is Status codes: * - valid, ^ - VPN best, > - best, d - damped, h - history, i - internal, s - suppressed, S - Stale Origin : i - IGP, e - EGP,? - incomplete Network NextHop MED LocPrf PrefVal Path/Ogn * >i / i * > i * i i * > i * i i R1(bgp)# show ip bgp 43
46 Local AS : 6500 Local Router-id : BGP Table Version : 0 Status codes: * - valid, > - best, i - internal, e - external, s - stale Origin codes: i - IGP, e - EGP,? - incomplete Network Nexthop Metric LocalPref Weight AsPath *> / i *> / i The BGP routing table of R1 now shows that it is announcing routes and since they are marked as best routes. Now, ping R2 from R3. <R3>ping PING : 56 data bytes, press CTRL_C to break Reply from : bytes=56 Sequence=1 ttl=254 time=1 ms Reply from : bytes=56 Sequence=2 ttl=254 time=1 ms Reply from : bytes=56 Sequence=3 ttl=254 time=1 ms Reply from : bytes=56 Sequence=4 ttl=254 time=1 ms Reply from : bytes=56 Sequence=5 ttl=254 time=1 ms ping statistics packet(s) transmitted 5 packet(s) received 0.00% packet loss round-trip min/avg/max = 1/1/1 ms R3 is receiving a successful ping reply. R3(bgp)# ping is alive, time = 4 ms Next-hop-local/next-hop-self command is missing An example of next-hop-local/next-hop-self command is missing is shown in Figure
47 Figure 15 Next-hop-local/next-hop-self command is missing Router R5 is an IBGP neighbor of R2 whereas R2 and R1 are EBGP neighbors. R5 is trying to ping network in AS Routes from AS 6500 appear in the BGP routing table, however they are not installed into the router s global IP routing table. Troubleshooting Verify the BGP routing table of R5. <R5>disp bgp routing-table Total Number of Routes: 3 BGP Local router ID is Status codes: * - valid, ^ - VPN best, > - best, d - damped, h - history, i - internal, s - suppressed, S - Stale Origin : i - IGP, e - EGP,? - incomplete Network NextHop MED LocPrf PrefVal Path/Ogn * i / i i i i ? R5(bgp)# show ip bgp Local AS : 777 Local Router-id : BGP Table Version : 4 45
48 Status codes: * - valid, > - best, i - internal, e - external, s - stale Origin codes: i - IGP, e - EGP,? - incomplete Network Nexthop Metric LocalPref Weight AsPath *> / i * i / i i / i i / i R5 is receiving the external-as routes from AS However, they are not being installed in the routing table. When AS 777 receives the routes, the NEXT_HOP attribute is set to the outgoing interface of R1 ( ). By default the NEXT_HOP attribute is preserved inside an AS. However, routes to /24 and /24 cannot be installed into the global routing table, since there is no route to in the global routing table already. [R5]ping PING : 56 data bytes, press CTRL_C to break Request time out Request time out Request time out Request time out Request time out Solution ping statistics packet(s) transmitted 0 packet(s) received % packet loss R5(bgp)# ping The destination address is unreachable. Add the command peer x.x.x.x next-hop-local or neighbor x.x.x.x next-hop-self under the BGP configuration of R2. This changes the next-hop for external-as routes to R2 for all the IBGP neighbors in AS 777. Since a route to R2 exists in AS 777, the route is installed in the global routing table. [R2]bgp 777 [R2-bgp]peer next-hop-local 46
49 R2(bgp)# router bgp 777 R2(bgp)# neighbor next-hop-self Verification Verify the BGP routing table of R5 [R5]disp bgp routing-table Total Number of Routes: 3 BGP Local router ID is Status codes: * - valid, ^ - VPN best, > - best, d - damped, h - history, i - internal, s - suppressed, S - Stale Origin : i - IGP, e - EGP,? - incomplete Network NextHop MED LocPrf PrefVal Path/Ogn * i / i * >i i * >i ? R5(bgp)# show ip bgp Local AS : 777 Local Router-id : BGP Table Version : 5 Status codes: * - valid, > - best, i - internal, e - external, s - stale Origin codes: i - IGP, e - EGP,? - incomplete Network Nexthop Metric LocalPref Weight AsPath * i / i *>i / i *>i / i R5 is now receiving the external-as routes with the next hop as which is R2 s interface ip. [R5]ping PING : 56 data bytes, press CTRL_C to break Reply from : bytes=56 Sequence=0 ttl=254 time=1 ms Reply from : bytes=56 Sequence=1 ttl=254 time=1 ms Reply from : bytes=56 Sequence=2 ttl=254 time=1 ms Reply from : bytes=56 Sequence=3 ttl=254 time=1 ms Reply from : bytes=56 Sequence=4 ttl=254 time=1 ms 47
50 ping statistics packet(s) transmitted 5 packet(s) received 0.00% packet loss round-trip min/avg/max = 1/1/1 ms R5(bgp)# ping is alive, time = 3 ms R5 is able to successfully ping the network in AS As an alternative solution, the IGP in AS777 could be configured to have a route to R1 ( ). This could be achieved by use of static routes or by injecting the route to into your IGP. However, the solution presented above (next-hop-self, next-hop-local) is generally preferable. BGP router not advertising the routes The most common reason for this is, the Router is not configured as Route Reflector for IBGP neighbors. Router is not receiving External-AS routes or routes that are more than one hop away. An example of router is not receiving external-as routes, is shown in Figure
51 Figure 16 router is not receiving external-as routes Problem R4 is not able to reach the network /24 in AS 777. Troubleshooting Check the IP routing table of R4 [R4]disp ip routing-table Routing Tables: Public Destinations : 5 Routes : 5 Destination/Mask Proto Pre Cost NextHop Interface /8 Direct InLoop /32 Direct InLoop /24 BGP GE0/ /24 Direct GE0/ /32 Direct InLoop0 R4(bgp)# show ip route IP Route Entries Destination Gateway VLAN Type Sub-Type Metric Dist. 49
52 /32 lo0 connected /8 reject static /32 lo0 connected / bgp /24 DEFAULT_VLAN 1 connected 1 0 Verify the BGP routing table of R4 to check whether R4 is receiving the External-as routes. [R4]disp bgp routing-table Total Number of Routes: 3 BGP Local router ID is Status codes: * - valid, ^ - VPN best, > - best, d - damped, h - history, i - internal, s - suppressed, S - Stale Origin : i - IGP, e - EGP,? - incomplete Network NextHop MED LocPrf PrefVal Path/Ogn * >i i * > i * i i R4(bgp)# show ip bgp Local AS : 6500 Local Router-id : BGP Table Version : 2 Status codes: * - valid, > - best, i - internal, e - external, s - stale Origin codes: i - IGP, e - EGP,? - incomplete Network Nexthop Metric LocalPref Weight AsPath *>i / i i / i R4 is not receiving any external-as routes. Check the routing table of R3 to verify whether it is receiving any external AS routes. 50
53 [R3]disp bgp routing-table Total Number of Routes: 5 BGP Local router ID is Status codes: * - valid, ^ - VPN best, > - best, d - damped, h - history, i - internal, s - suppressed, S - Stale Origin : i - IGP, e - EGP,? - incomplete Network NextHop MED LocPrf PrefVal Path/Ogn * >i / i * > i * i i * > i * i i R3(bgp)# show ip bgp Local AS : 6500 Local Router-id : BGP Table Version : 4 Status codes: * - valid, > - best, i - internal, e - external, s - stale Origin codes: i - IGP, e - EGP,? - incomplete Network Nexthop Metric LocalPref Weight AsPath * i / i * i / i *> / i R3 is receiving the external-as routes. But R4 is not receiving the same routes. Check the BGP configuration on R3. [R3]disp current-configuration begin bgp bgp 6500 network network undo synchronization peer as-number 6500 peer as-number 6500 R3(bgp)# show run router bgp 6500 enable network network
54 neighbor remote-as 6500 neighbor remote-as 6500 exit Solution R3 is an IBGP neighbor of R1. Even though R3 receives all the external-as routes from R1, it does not advertise those routes to R4. IBGP rules state that IBGP routes that are learned from another peer are not propagated. To advertise these external-as routes to other IBGP neighbors in AS 6500, configure R3 as Route reflector for all routers in the AS. A route reflector acts as a hub for IBGP peers, allowing them to exchange routes directly with each other. Configure R3 as Route reflector for R4 and R1. [R3]bgp 6500 [R3-bgp]peer reflect-client [R3-bgp]peer reflect-client R3(bgp)# router bgp 6500 R3(bgp)# neighbor route-reflector-client R3(bgp)# neighbor route-reflector-client Verification Verify whether R4 is receiving the external-as routes. [R4]disp bgp routing-table Total Number of Routes: 4 BGP Local router ID is Status codes: * - valid, ^ - VPN best, > - best, d - damped, h - history, i - internal, s - suppressed, S - Stale Origin : i - IGP, e - EGP,? - incomplete Network NextHop MED LocPrf PrefVal Path/Ogn * >i / i * >i i * > i * i i R4(bgp)# show ip bgp 52
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