bgp next-hop

Answered Question
Nov 2nd, 2009
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hello,


i getting one issue regarding external network reachability issue from ibgp peers.


R1 and R2 are EBGP nei

R2, R3 and R4 are full mesh ibgp nei

EIGRP is running between R2 R3 and R4


on R2, next-hop-self command used for R3 and R4 for external netwrk 192.168.1.0/24 which is commected loopback interface of R1


issue-- i can able to see 192.168.1.0 in bgp and routing table of R2 R3 and R4 and able to ping from R2 but unable to ping from R3 and R4 and its stuck till R2


please suggest...

Correct Answer by Giuseppe Larosa about 7 years 6 months ago

hello Sourabth,

the alternate way is to use the network command in router BGP on R2.


in BGP network command behaves differently then with IGPs like EIGRP:

network command can be used to put into BGP table every IP prefix known in the IP routing table including prefixes learned by EIGRP, OSPF and so on.


so you need to use

network prefix mask


for example for 172.16.20.0/24


use

network 172.16.20.0 mask 255.255.255.0


the usage of mask is mandatory if you have disabled auto-summary with

no auto-summary


this command changes the behaviour of network command.

with no auto-summary an exact match in IP routing table is needed to trigger injection into BGP table


Hope to help

Giuseppe


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Giuseppe Larosa Mon, 11/02/2009 - 05:58
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Hello Sourabh,

with next-hop-self you have been able to make R3 and R4 to accept eBGP route 192.168.1.0/24.


However, R1 may need routing information to be able to send the ICMP echo reply back to R3,R4.

so using debug ip icmp or simply using sh ip route 192.168.1.0 on R3 and R4 verify what is the source IP address they use in their ICMP echo requests.


on R2 you may need additional network commands to be used to advertise internal networks to R1.


Hope to help

Giuseppe


sourabh1000_2 Mon, 11/02/2009 - 06:52
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hello Giuseppe


now i am able to ping 192.168.1.1 from R3 and R4 after redistributing EIGRP into BGP on R2, but why i require redistribution, is there any another alternate way to reach external netorks without doing redistribution??

Correct Answer
Giuseppe Larosa Mon, 11/02/2009 - 07:11
User Badges:
  • Super Silver, 17500 points or more
  • Hall of Fame,

    Founding Member

hello Sourabth,

the alternate way is to use the network command in router BGP on R2.


in BGP network command behaves differently then with IGPs like EIGRP:

network command can be used to put into BGP table every IP prefix known in the IP routing table including prefixes learned by EIGRP, OSPF and so on.


so you need to use

network prefix mask


for example for 172.16.20.0/24


use

network 172.16.20.0 mask 255.255.255.0


the usage of mask is mandatory if you have disabled auto-summary with

no auto-summary


this command changes the behaviour of network command.

with no auto-summary an exact match in IP routing table is needed to trigger injection into BGP table


Hope to help

Giuseppe


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