EE627 Lecture 22. Multihoming Route Control Devices

Transcription

1 EE627 Lecture 22 Multihoming Route Control Devices 1

2 Multihoming Connect to multiple ISPs Provide reliability from access link/isp failures Potential for load balancing Intelligent Route Control Devices Manage multiple ISP connections more intelligently Load balancing Choose the best path to destination 2

3 Route Control Devices Source: telechoice.com 3

4 Route Control Devices 4

5 Steps in route control 5

6 Route Control How? NAT based Necessary when end user/network do not have independent address block Each ISP provides the user its own address Choice of address determines the choice of ISP Translate internal address (source) of an outgoing packet to the address given by chosen ISP 6

7 Route Control How? BGP based Advertise different addresses to different ISPs Outgoing traffic can choose any of the ISPs If no ingress filtering used Incoming traffic depends on traffic to different addresses If not all addresses advertised to all ISPs Service disruption possible 7

8 Route Control Advertise all addresses to all ISPs More robust Outgoing traffic can be still controlled by a local router No control on incoming traffic BGP relationships determine the traffic volumes 8

9 Outgoing traffic Control RCD can choose WFQ or stateful forwarding Hash 5-tuple of flow into one outgoing link Measure performance to destinations and use that information in choosing paths Build a routing table for each destination 9

10 Incoming Route Control DNS announcements Announce reachability information selectively to each ISP Some addresses are visible only through one ISP Users trying to access that IP address are forced to come through that ISP Route control at coarse time granularity 10

11 Incoming Route Control Have multiple base web pages One for each ISP The embedded objects within a page employ IP addresses of the particular ISP When users access embedded objects, they will use different ISPs to access content 11

12 Passive Measurement Monitor ongoing connections Measure the RTTs Typically the SYN, ACK pair Maintain a database Limit it to popular web sites If info. available on all links, choose best one If info. is stale on one of the links, initiate a measurement by opening a new connection 12

13 Active Measurement Maintain a list of active destinations Use frequency counts or a sliding window Actively probe the paths to these destinations every sampling interval 13

14 Performance benefits Observed from 15-40% improvement based on number of ISPs About 4 ISPs shown to provide all the improvement you can get 14

15 Link failures What to do on link failures? Why is this any different than in telephone networks? Phone networks provide very high reliability Use dynamic routing on link failures IP routing has some delays Link state propagation Computing new routing tables Loading forward information bases (FIBs) 15

16 Link failures Measurements in Sprint network observed that link failures can take 6-30 seconds to reroute Can t afford to wait that long for repair Voice/video flows will be disrupted How to improve routing during failures? 16

17 Derouting Send packet along another hop than default nexthop Hope that it eventually gets to destination Can have routing loops How to do this while guaranteeing no loops 17

18 An example for derouting 18

19 General Approach Case 1 19

20 General Approach Case 2 20

21 How well does this work? 21

22 Derouting performance 22

23 Derouting issues For some link failures, may not have a solution with this approach Not universal Alternate approaches can find solutions Can also deal with multiple equal cost paths Look at references 23

24 Summary Multihoming and route control devices can help improve reliability and performance IP networks need mechanisms for quick failover Derouting is one approach 24