EIGRP Route Summarization
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- By default, EIGRP has auto summarization enabled which summarizes routes to classful boundaries, but this can cause issues, so EIGRP allows manual summarization at arbitrary boundaries using the ip summary-address command. - Manual summarization can be configured on any router or interface in an EIGRP domain. A summary route will exist as long as there is at least one more specific route; if the last specific route disappears, the summary will also disappear. - The document provides an example configuration of EIGRP routing between four routers (R1, R2, R3, R4) with the configuration of manual summarization on R2's S0/0 interface to summarize routes
![• IF YOU WANT TO USE AUTO-SUMMARIZATION YOU HAVE TO DO
NOTHING BECAUSE IT IS ENABLED BY DEFAULT, OTHERWISE USE NO
AUTO-SUMMARY EIGRP COMMAND TO DISABLE IT.
• TO DO MANUAL SUMMARIZATION GO UNDER INTERFACE AND
USE IP SUMMARY-ADDRESS EIGRP AS-NUMBER ADDRESS MASK
[ADMINISTRATIVE-DISTANCE ] COMMAND.](https://image.slidesharecdn.com/eigrproutesummarization-161010045203/85/EIGRP-Route-Summarization-3-320.jpg)
![LET’S CHECK NOW R1’S ROUTING TABLE
• R1#SH IP ROUTE
• ... OUTPUT OMMITED ...
• GATEWAY OF LAST RESORT IS NOT SET
• D 192.168.8.0/24 [90/2195456] VIA 192.168.0.1, 00:00:12,
SERIAL0/0
• D 192.168.9.0/24 [90/2323456] VIA 192.168.0.1, 00:00:12,
SERIAL0/0
• D 192.168.10.0/24 [90/2195456] VIA 192.168.0.1, 00:00:12,
SERIAL0/0
• D 192.168.11.0/24 [90/2323456] VIA 192.168.0.1, 00:00:12,
SERIAL0/0](https://image.slidesharecdn.com/eigrproutesummarization-161010045203/85/EIGRP-Route-Summarization-9-320.jpg)
![CHECK ROUTING TABLE ON R1AGAIN
• R1#SH IP ROUTE
• ... OUTPUT OMMITED ...
• GATEWAY OF LAST RESORT IS NOT SET
• C 192.168.0.0/24 IS DIRECTLY CONNECTED, SERIAL0/0
• D 192.168.8.0/21 [90/2195456] VIA 192.168.0.1, 00:01:42,
SERIAL0/0
• R1#
• ALL ROUTES LEARNED FROM R1 ARE NOW SUMMARIZED AND THE
METRIC IS 2195456, THE SMALLEST METRIC OF THE SPECIFIC
ROUTES](https://image.slidesharecdn.com/eigrproutesummarization-161010045203/85/EIGRP-Route-Summarization-11-320.jpg)
![• R2#SHOW IP ROUTE
• ... OUTPUT OMMITED ...
• GATEWAY OF LAST RESORT IS NOT SET
• C 192.168.8.0/24 IS DIRECTLY CONNECTED,
FASTETHERNET0/1
• D 192.168.9.0/24 [90/409600] VIA 192.168.8.2, 01:04:43,
FASTETHERNET0/1
• C 192.168.10.0/24 IS DIRECTLY CONNECTED,
FASTETHERNET0/0
• D 192.168.11.0/24 [90/409600] VIA 192.168.10.2, 01:04:43,
FASTETHERNET0/0
• C 192.168.0.0/24 IS DIRECTLY CONNECTED, SERIAL0/0](https://image.slidesharecdn.com/eigrproutesummarization-161010045203/85/EIGRP-Route-Summarization-12-320.jpg)
EIGRP Route Summarization
- 2. • BY DEFAULT EIGRP HAS AUTO SUMMARIZATION ENABLED. THIS MEANS THAT IT WILL SUMMARIZE TO CLASSFUL ADDRESSES AT NETWORK BOUNDARIES. • LEAVING AUTO SUMMARIZATION ENABLED COULD CAUSE A LOT OF TROUBLES IN OUR NETWORK. EIGRP HAS THE ABILITY TO CREATE SUMMARY ROUTES AT ARBITRARY BOUNDARIES BY USING MANUAL SUMMARIZATION. • MANUAL SUMMARIZATION CAN BE APPLIED ANYWHERE IN EIGRP DOMAIN, ON EVERY ROUTER, ON EVERY INTERFACE. • SUMMARY ROUTE WILL EXIST IN ROUTING TABLE AS LONG AS AT LEAST ONE MORE SPECIFIC ROUTE WILL EXIST. IF THE LAST SPECIFIC ROUTE WILL DISAPPEAR, SUMMARY ROUTE ALSO WILL
- 3. • IF YOU WANT TO USE AUTO-SUMMARIZATION YOU HAVE TO DO NOTHING BECAUSE IT IS ENABLED BY DEFAULT, OTHERWISE USE NO AUTO-SUMMARY EIGRP COMMAND TO DISABLE IT. • TO DO MANUAL SUMMARIZATION GO UNDER INTERFACE AND USE IP SUMMARY-ADDRESS EIGRP AS-NUMBER ADDRESS MASK [ADMINISTRATIVE-DISTANCE ] COMMAND.
- 5. • UNLIKE OSPF WHERE WE CAN SUMMARIZE ONLY ON ABR OR ASBR IN EIGRP WE CAN SUMMARIZE ANYWHERE. WE WILL DO THIS ON R2’S S0/0 INTERFACE, SO A SUMMARY ROUTE WILL BE SENT TO R1. FIRST WILL CONFIGURE EIGRP TO RUN IN THIS NETWORK. R1 • R1(CONFIG)#INTERFACE SERIAL 0/0 • R1(CONFIG-IF)#IP ADDRESS 192.168.0.2 255.255.255.0 • R1(CONFIG-IF)#NO SHUTDOWN • R1(CONFIG)#ROUTER EIGRP 1 • R1(CONFIG-ROUTER)#NO AUTO-SUMMARY • R1(CONFIG-ROUTER)#NETWORK 192.168.0.0
- 6. R2 • R2(CONFIG)#INTERFACE SERIAL 0/0 • R2(CONFIG-IF)#IP ADDRESS 192.168.0.1 255.255.255.0 • R2(CONFIG-IF)#NO SHUTDOWN • R2(CONFIG-IF)#INTERFACE FA0/0 • R2(CONFIG-IF)#IP ADDRESS 192.168.10.1 255.255.255.0 • R2(CONFIG-IF)#NO SHUTDOWN • R2(CONFIG-IF)#INTERFACE FA0/1 • R2(CONFIG-IF)#IP ADDRESS 192.168.8.1 255.255.255.0 • R2(CONFIG-IF)#NO SHUTDOWN • R2(CONFIG)#ROUTER EIGRP 1 • R2(CONFIG-ROUTER)#NO AUTO-SUMMARY • R2(CONFIG-ROUTER)#NETWORK 192.168.0.0 • R2(CONFIG-ROUTER)#NETWORK 192.168.8.0 • R2(CONFIG-ROUTER)#NETWORK 192.168.10.0
- 7. R3 • R3(CONFIG)#INTERFACE FASTETHERNET 0/0 • R3(CONFIG-IF)#IP ADDRESS 192.168.10.2 255.255.255.0 • R3(CONFIG-IF)#NO SHUTDOWN • R3(CONFIG-IF)#INTERFACE LOOPBACK 0 • R3(CONFIG-IF)#IP ADDRESS 192.168.11.1 255.255.255.0 • R3(CONFIG)#ROUTER EIGRP 1 • R3(CONFIG-ROUTER)#NO AUTO-SUMMARY • R3(CONFIG-ROUTER)#NETWORK 192.168.10.0 • R3(CONFIG-ROUTER)#NETWORK 192.168.11.0
- 8. R4 • R4(CONFIG)#INTERFACE FASTETHERNET 0/0 • R4(CONFIG-IF)#IP ADDRESS 192.168.8.2 255.255.255.0 • R4(CONFIG-IF)#NO SHUTDOWN • R4(CONFIG-IF)#INTERFACE LOOPBACK 0 • R4(CONFIG-IF)#IP ADDRESS 192.168.9.1 255.255.255.0 • R4(CONFIG)#ROUTER EIGRP 1 • R4(CONFIG-ROUTER)#NO AUTO-SUMMARY • R4(CONFIG-ROUTER)#NETWORK 192.168.8.0 • R4(CONFIG-ROUTER)#NETWORK 192.168.9.0
- 9. LET’S CHECK NOW R1’S ROUTING TABLE • R1#SH IP ROUTE • ... OUTPUT OMMITED ... • GATEWAY OF LAST RESORT IS NOT SET • D 192.168.8.0/24 [90/2195456] VIA 192.168.0.1, 00:00:12, SERIAL0/0 • D 192.168.9.0/24 [90/2323456] VIA 192.168.0.1, 00:00:12, SERIAL0/0 • D 192.168.10.0/24 [90/2195456] VIA 192.168.0.1, 00:00:12, SERIAL0/0 • D 192.168.11.0/24 [90/2323456] VIA 192.168.0.1, 00:00:12, SERIAL0/0
- 10. • LOOK TO THE METRICS OF LEARNED ROUTES, AND AFTER WE DO SUMMARIZATION, WILL COMPARE THIS ONE WITH THAT SUMMARY METRIC. NOW WE WILL DO SUMMARIZATION ON R2’S S0/0 INTERAFCE. • R2(CONFIG-IF)#IP SUMMARY-ADDRESS EIGRP 1 192.168.8.0 255.255.248.0
- 11. CHECK ROUTING TABLE ON R1AGAIN • R1#SH IP ROUTE • ... OUTPUT OMMITED ... • GATEWAY OF LAST RESORT IS NOT SET • C 192.168.0.0/24 IS DIRECTLY CONNECTED, SERIAL0/0 • D 192.168.8.0/21 [90/2195456] VIA 192.168.0.1, 00:01:42, SERIAL0/0 • R1# • ALL ROUTES LEARNED FROM R1 ARE NOW SUMMARIZED AND THE METRIC IS 2195456, THE SMALLEST METRIC OF THE SPECIFIC ROUTES
- 12. • R2#SHOW IP ROUTE • ... OUTPUT OMMITED ... • GATEWAY OF LAST RESORT IS NOT SET • C 192.168.8.0/24 IS DIRECTLY CONNECTED, FASTETHERNET0/1 • D 192.168.9.0/24 [90/409600] VIA 192.168.8.2, 01:04:43, FASTETHERNET0/1 • C 192.168.10.0/24 IS DIRECTLY CONNECTED, FASTETHERNET0/0 • D 192.168.11.0/24 [90/409600] VIA 192.168.10.2, 01:04:43, FASTETHERNET0/0 • C 192.168.0.0/24 IS DIRECTLY CONNECTED, SERIAL0/0
- 13. • WHEN YOU CONFIGURE AN EIGRP SUMMARY ROUTE, THAT ROUTE WILL APPEAR ON GENERATING ROUTER ALSO, BUT WITH NEXT HOP NULL0 WHICH IS A SOFTWARE INTERFACE. • NULL0 INTERFACE IS USED TO PREVENT PACKETS FROM BEING SENT FURTHER IF THE ROUTER DOESN'T HAVE A SPECIFIC ROUTE, THUS WILL DENY PACKETS TO GO THROUGH THE NETWORK.