Route Optimization. Seed Metrics and Route Redistribution. BSCI Module Cisco Systems, Inc. All rights reserved.

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1 Route Optimization BSCI Module 5 1 Seed Metrics and Route Redistribution BSCI Module Cisco Systems, Inc. All rights reserved. Cisco Public 2 1

2 Using Multiple IP Routing Protocols 3 Redistribution with Seed Metric 4 2

3 Default Seed Metrics Protocol RIP IGRP/EIGRP OSPF IS-IS BGP Default Seed Metrics Infinity Infinity 20 for all except BGP, which is 1 0 BGP metric is set to IGP metric value 5 Configuring and Verifying Route Redistribution BSCI Module Cisco Systems, Inc. All rights reserved. Cisco Public 6 3

4 Redistribution Supports All Protocols RtrA(config)#router rip RtrA(config-router)#redistribute? bgp Border Gateway Protocol (BGP) connected Connected eigrp Enhanced Interior Gateway Routing Protocol (EIGRP) isis ISO IS-IS iso-igrp IGRP for OSI networks metric Metric for redistributed routes mobile Mobile routes odr On Demand stub Routes ospf Open Shortest Path First (OSPF) rip Routing Information Protocol (RIP) route-map Route map reference static Static routes <cr> 7 Planning Redistribution Locate the boundary router between two routing processes. Determine which routing process is the core or backbone process Determine which routing process is the edge or migration process Select a method for injecting the required edge protocol routes into the core. 8 4

5 Configuring Redistribution into RIP Use this command to redistribute routes into RIP: Router(config-router)# redistribute protocol [process-id] [match route-type] [metric metricvalue] [route-map map-tag] RtrA(config)# router rip RtrA(config-router)# redistribute ospf? < > Process ID RtrA(config-router)# redistribute ospf 1? match Redistribution of OSPF routes metric Metric for redistributed routes route-map Route map reference <cr> Default metric is infinity. 9 Redistribute command Router(config-router)# redistribute protocol [process-id] {level-1 level-1-2 level-2} [metric metric-value] [metric-type type-value] [match {internal external 1 external 2}] [tag tag-value] [route-map map-tag] [weight weight] [subnets] Redistribute static [ip]: It is used to redistribute IP static routes. The optional ip keyword is used when redistributing into the Intermediate System-to-Intermediate System (IS-IS) protocol. Redistribute connected: It refers to routes that are established automatically by virtue of having enabled IP on an interface. (Optional) metric: Used for the redistributed route. If a value is not specified for this option, and no value is specified using the default-metric command, the default metric value is 0 for IS-IS and 20 for OSPF. (Optional) metric-type For OSPF. It can : 1-Type 1 external route, 2-Type 2 external route 10 5

6 Redistributing into RIP 11 Configuring Redistribution into OSPF Use this command to redistribute routes into OSPF: Router(config-router)# redistribute protocol [process-id] [metric metric-value] [metric-type type-value] [route-map map-tag] [subnets] [tag tag-value] Default metric is 20. Default metric type is 2. Subnets do not redistribute by default. 12 6

7 Example: Redistribution into OSPF RtrA(config)# router ospf 1 RtrA(config-router)# redistribute eigrp? < > Autonomous system number RtrA(config-router)# redistribute eigrp 100? metric Metric for redistributed routes metric-type OSPF/IS-IS exterior metric type for redistributed routes route-map Route map reference subnets Consider subnets for redistribution into OSPF tag Set tag for routes redistributed into OSPF <cr> 13 Redistributing into OSPF 14 7

8 Configuring Redistribution into EIGRP Use this command to redistribute routes into EIGRP: router(config-router)# redistribute protocol [process-id] [match {internal external 1 external 2}] [metric metric-value] [route-map map-tag] RtrA(config)# router eigrp 100 RtrA(config-router)# redistribute ospf? < > Process ID RtrA(config-router)# redistribute ospf 1? match Redistribution of OSPF routes metric Metric for redistributed routes route-map Route map reference <cr> Default metric is infinity. 15 Redistributing into EIGRP Bandwidth in kilobytes = Delay in tens of microseconds = 100 Reliability = 255 (maximum) Load = 1 (minimum) MTU = 1,500 bytes 16 8

9 Configuring Redistribution into IS-IS Use this command to redistribute routes into IS-IS: router(config-router)# redistribute protocol [process-id] [level level-value] [metric metric-value] [metric-type type-value] [routemap map-tag] RtrA(config)# router isis RtrA(config-router)# redistribute eigrp 100? level-1 IS-IS level-1 routes only level-1-2 IS-IS level-1 and level-2 routes level-2 IS-IS level-2 routes only metric Metric for redistributed routes metric-type OSPF/IS-IS exterior metric type for redistributed routes route-map Route map reference.. Output Omitted Routes are introduced as level 2 with a metric of 0 by default. 17 Redistributing into IS-IS 18 9

10 Redistributing IS-IS into Other Protocols Router(config)# router ospf 1 Router(config-router)# redistribute isis? <output omitted> level-1 IS-IS level-1 routes only level-1-2 IS-IS level-1 and level-2 routes level-2 IS-IS level-2 routes only <output omitted> 19 Route Redistribution Example BSCI Module Cisco Systems, Inc. All rights reserved. Cisco Public 20 10

11 Example: Before Redistribution 21 Example: Before Redistribution (Cont.) 22 11

12 Example: Configuring Redistribution at Router B 23 Example: Routing Tables After Route Redistribution 24 12

13 Example: Routing Tables After Summarizing Routes and Redistributions 25 Modifying Administrative Distance 26 13

14 Administrative Distance A routing protocol s administrative distance rates its trustworthiness as a source of routing information. It is an integer from 0 to 255. The lowest administrative distance has the highest trust rating. An administrative distance of 255 means the routing information source cannot be trusted at all and should be ignored. An administrative distance of zero is reserved for connected interfaces, and will always be preferred. 27 Administrative Distance Good CCNP Routing Exam Knowledge! 28 14

15 Administrative Distance When using multiple IP routing protocols on a router, the default distances almost always suffice. However, some circumstances call for changing the administrative distance values on a router. If, for example, a router is running both IGRP and OSPF, it may receive routes to the same network from both protocols. The default administrative distances favor IGRP routes over OSPF routes: IGRP at 100 favored I [100/10576] via , Serial [110/192] via , Serial1 29 Changing Administrative Distance But since IGRP doesn t support CIDR, you may want the router to use the OSPF route instead. In this case, you can configure the local router to apply a custom administrative distance to all OSPF routes: RTZ(config)#router ospf 1 RTZ(config-router)#distance 95 OSPF at 95 now favored I [100/10576] via , Serial [ 95/192] via , Serial

16 Changing Administrative Distance You can also apply the distance command with optional arguments to make changes to selected routes based on where they originate. The expanded syntax of the distance command is as follows: Router(config-router)#distance weight [source-ip-address source-mask (access-list-number name)] For example, we can configure a router to apply an administrative distance of 105 to all RIP routes received from These values are local to the router, all other routers will apply the administrative distance of 120. RTZ(config)#router rip RTZ(config-router)#distance Changing Administrative Distance Or, we can configure a router to apply an administrative distance of 97 to specific RIP routes, , received from RTZ(config)#router rip RTZ(config-router)#distance RTZ(config-router)#exit Source of the route RTZ(config)#access-list 2 permit The route that will get the administrative distance of

17 Controlling Routing Update Traffic BSCI Module Cisco Systems, Inc. All rights reserved. Cisco Public 33 Using the passive-interface Command 34 17

18 Passive Interfaces The passive-interface command works differently with the different IP routing protocols that support it. RIP/IGRP: Can receive updates but doesn t send. OSPF: Routing information is neither sent nor received via a passive interface. OSPF: The network address of the passive interface appears as a stub network in the OSPF domain. EIGRP: the router stops sending hello packets on passive interfaces. When this happens, the EIGRP router can t form neighbor adjacencies on the interface or send and receive routing updates. 35 Route Filters Configuring an interface as passive prevents it from sending updates entirely There are times when you need to suppress only certain routes in the update from being sent or received. We can use a distribute-list command to pick and choose what routes a router will send or receive updates about. The distribute-list references an access-list, which creates a route filter a set of rules that precisely controls what routes a router sends or receives in a routing update

19 Route Filters Let s take a look on how keep subnet from entering RTZ! 37 Route Filters Inbound interfaces: When applied to inbound updates, the syntax for configuring a route filter is: Router(config-router)#distribute-list access-listnumber in [interface-name] Note: This does not permit/deny packets from entering the routers, only what routes a router will send or receive updates about

20 Inbound Route Filters (global) Applies to all interfaces RTZ(config)#router rip RTZ(config-router)#network RTZ(config-router)#distribute-list 16 in RTZ(config)#access-list 16 deny RTZ(config)#access-list 16 permit any 39 Inbound Route Filters (interface) RTZ(config)#router rip Applies to just S0 interface RTZ(config-router)#network RTZ(config-router)#distribute-list 16 in s0 RTZ(config)#access-list 16 deny RTZ(config)#access-list 16 permit any 40 20

21 Route Filters Outbound interfaces: When applied to outbound updates, the syntax can be more complicated: Router(config-router)#distribute-list access-listnumber out [interface-name routing-process asnumber] 41 Outbound Route Filters (global) Applies to all interfaces Applies to all interfaces although this graphic only shows S2. RTA(config)#router rip RTA(config-router)#network RTA(config-router)#distribute-list 24 out RTA(config)#access-list 24 deny RTA(config)#access-list 24 permit any 42 21

22 Outbound Route Filters (interface) RTA(config)#router rip RTA(config-router)#network RTA(config-router)#distribute-list 24 out s2 RTA(config)#access-list 24 deny RTA(config)#access-list 24 permit any Applies to just S2 interface 43 Route Filters For each interface and routing process, Cisco IOS permits one incoming global, one outgoing global, one incoming interface, and one outgoing interface distribute-list: RTZ(config)#router rip RTZ(config-router)#distribute-list 1 in RTZ(config-router)#distribute-list 2 out RTZ(config-router)#distribute-list 3 in e0 RTZ(config-router)#distribute-list 4 out e

23 Passive EIGRP interfaces A passive interface can t send EIGRP hellos, which thus prevents adjacency relationships with link partners. An administrator can create a pseudo passive EIGRP interface by using a route filter that suppresses all routes from the EIGRP routing update. RTA(config)#router eigrp 364 RTA(config-router)#network RTA(config-router)#distribute-list 5 out s0 RTA(config-router)#exit RTA(config)#access-list 5 deny any 45 Policy Based Routing 46 23

24 Route Maps Route maps are similar to a scripting language for these reasons: They work like a more sophisticated access list: Top-down processing Once there is a match, leave the route map Lines are sequence-numbered for easier editing: Insertion of lines Deletion of lines Route maps are named rather than numbered for easier documentation. Match criteria and set criteria can be used, similar to the if, then logic in a scripting language. 47 Route Map Applications The common uses of route maps are as follows: Redistribution route filtering: A more sophisticated alternative to distribute lists Policy-based routing: The ability to determine routing policy based on criteria other than the destination network BGP policy implementation: The primary tool for defining BGP routing policies 48 24

25 Route Map Operation A list of statements composes a route map. The list is processed top-down like an access list. The first match found for a route is applied. The sequence number is used for inserting or deleting specific route map statements. route-map my_bgp permit 10 { match statements } { match statements } { set statements } { set statements } route-map my_bgp deny 20 :: :: :: :: :: :: route-map my_bgp permit 30 :: :: :: :: :: :: 49 Route Map Operation (Cont.) The match statement may contain multiple references. Multiple match criteria in the same line use a logical OR. At least one reference must permit the route for it to be a candidate for redistribution. Each vertical match uses a logical AND. All match statements must permit the route for it to remain a candidate for redistribution. Route map permit or deny determines if the candidate will be redistributed

26 The match Command The match commands specify criteria to be matched. The associated route map statement permits or denies the matching routes. router(config-route-map)# match {options} options : ip address ip-access-list ip route-source ip-access-list ip next-hop ip-access-list interface type number metric metric-value route-type [external internal level-1 level-2 local] 51 The match commands Command match community match interface match ip address match ip nexthop match ip routesource match length match metric match route-type match tag Description Matches a BGP community Matches any routes that have the next hop out of one of the interfaces specified Matches any routes that have a destination network number address that is permitted by a standard or extended ACL Matches any routes that have a next-hop router address that is passed by one of the ACLs specified Matches routes that have been advertised by routers and access servers at the address that is specified by the ACLs Matches based on the layer 3 length of a packet Matches routes with the metric specified Matches routes of the specified type Matches tag of a route 52 26

27 The set Command The set commands modify matching routes. The command modifies parameters in redistributed routes. router(config-route-map)# set {options} options : metric metric-value metric-type [type-1 type-2 internal external] level [level-1 level-2 level-1-2 stub-area backbone] ip next-hop next-hop-address 53 The set commands Command set as-path set automatic-tag Description Modifies an AS path for BGP routes Computes automatically the tag value set community set default interface set interface set ip default next-hop set ip next-hop set level set local-preference set metric set metric-type set tag set weight Sets the BGP communities attribute Indicates where to output packets that pass a match clause of a route map for policy routing and have no explicit route to the destination Indicates where to output packets that pass a match clause of a route map for policy routing Indicates where to output packets that pass a match clause of a route map for policy routing and for which the Cisco IOS software has no explicit route to a destination Indicates where to output packets that pass a match clause of a route map for policy routing Indicates where to import routes for IS-IS and OSPF Specifies a BGP local preference value Sets the metric value for a routing protocol Sets the metric type for the destination routing protocol Sets tag value for destination routing protocol Specifies the BGP weight value 54 27

28 Route Maps and Redistribution Commands Router(config)# router ospf 10 Router(config-router)# redistribute rip route-map redis-rip Routes matching either access list 23 or 29 are redistributed with an OSPF cost of 500, external type 1. Routes permitted by access list 37 are not redistributed. All other routes are redistributed with an OSPF cost metric of 5000, external type 2. Router(config)# route-map redis-rip permit 10 match ip address set metric 500 set metric-type type-1 Router(config)# access-list 23 permit access-list 29 permit access-list 37 permit route-map redis-rip deny 20 match ip address 37 route-map redis-rip permit 30 set metric 5000 set metric-type type-2 55 Examples 56 28

29 Example: Redistribution Using Administrative Distance 57 Example: Redistribution Using Administrative Distance (Cont.) Router P3R1 router ospf 1 redistribute rip metric metric-type 1 subnets network area 0! router rip version 2 redistribute ospf 1 metric 5 network no auto-summary Router P3R2 router ospf 1 redistribute rip metric metric-type 1 subnets network area 0! router rip version 2 redistribute ospf 1 metric 5 network no auto-summary 58 29

30 Example: Redistribution Using Administrative Distance (Cont.) 59 Example: Redistribution Using Administrative Distance 60 30

31 Example: Redistribution Using Administrative Distance (Cont.) hostname P3R1! router ospf 1 redistribute rip metric metric-type 1 subnets network area 0 distance ! router rip version 2 redistribute ospf 1 metric 5 network no auto-summary! access-list 64 permit access-list 64 permit access-list 64 permit access-list 64 permit access-list 64 permit access-list 64 permit access-list 64 permit hostname P3R2! router ospf 1 redistribute rip metric metric-type 1 subnets network area 0 distance ! router rip version 2 redistribute ospf 1 metric 5 network no auto-summary! access-list 64 permit access-list 64 permit access-list 64 permit access-list 64 permit access-list 64 permit access-list 64 permit access-list 64 permit Example: Redistribution Using Administrative Distance (Cont.) hostname P3R1! router ospf 1 redistribute rip metric metric-type 1 subnets network area 0 distance ! router rip version 2 redistribute ospf 1 metric 5 network no auto-summary! access-list 64 permit access-list 64 permit access-list 64 permit access-list 64 permit access-list 64 permit access-list 64 permit access-list 64 permit hostname P3R2! router ospf 1 redistribute rip metric metric-type 1 subnets network area 0 distance ! router rip version 2 redistribute ospf 1 metric 5 network no auto-summary! access-list 64 permit access-list 64 permit access-list 64 permit access-list 64 permit access-list 64 permit access-list 64 permit access-list 64 permit

32 Example: Redistribution Using Administrative Distance (Cont.) 63 Know Your Network Be very familiar with your network BEFORE implementing redistribution Focus on routers with redundant paths Make sure no path information is lost when using the distance command 64 32

33 Configuring DHCP BSCI Module Cisco Systems, Inc. All rights reserved. Cisco Public 65 DHCP in an Enterprise Network 66 33

34 DHCP protocol 67 Configuring an Cisco IOS DHCP Server Router(config)#ip dhcp pool [pool name] Enable a DHCP pool for use by hosts. Router(config-dhcp)#network [network address][subnet mask] Specify the network and subnet mask of the pool. Router(config-dhcp)#default-router [host address] Specify the default router for the pool to use. Router(config)#ip dhcp excluded-address low-address high-address Specify the IP address that should not assign to DHCP clients

35 Optional DHCP Server Commands Router(config-dhcp)#domain-name domain Specifies the domain name for the client. Router(config-dhcp)#dns-server address Specifies the IP address of a DNS server that is available to a DHCP client. One is required, but up to eight can be specified. Router(config-dhcp)#netbios-name-server address Same as DNS, but for WINS. Router(config-dhcp)#lease {days [hours] [minutes] infinite} Specifies the duration of the lease. The default is a oneday lease. 69 DHCP Database Command and Configuration Router(config)#ip dhcp database url [timeout seconds writedelay seconds] Configures the database agent and the interval between database updates and database transfers. ip dhcp database ftp://user:passwords@ /router-dhcp write-delay 120 ip dhcp excluded-address ip dhcp excluded-address ip dhcp pool 0 network /16 domain-name global.com dns-server netbios-name-server default-router

36 Importing and Autoconfiguration RemoteRouter(config-dhcp)#import all Used to import DHCP option parameters from a centralized DHCP server. Used for remote DHCP pools. 71 Importing and Autoconfiguration (Cont.) ip dhcp-excluded address ip dhcp pool central network default-router domain name central.com dns-server netbios-name-server interface fastethernet0/0 ip address ip dhcp-excluded address ip dhcp pool client network default-router import all interface fastethernet0/0 ip address dhcp 72 36

37 DHCP Client Enables an IOS device to obtain an IP address dynamically from a DHCP server. Router (config-if)# ip address dhcp ip dhcp-excluded address ip dhcp pool client network default-router import all interface fastethernet0/0 ip address dhcp 73 IP helper address 74 37

38 Relay Agent Option Support Router (config)# ip dhcp relay information option 75 Q and A 76 38

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