EBGP default route

[petercinvest]

I have router R1, connect to ISP2, ISP2 is connected to ISP1.

ISP1 use neighbor default-originate command and give ISP2 a default B* 0.0.0.0 route, now I establish a ebgp relationship between R1 and ISP2.

but I didn't configure neighbor default-originate in ISP2,  will R1 receive a B* 0.0.0.0 route from ISP2? thanks

[Georg Pauwen]

Hello,

the short answer is yes, your R1 will receive the default route form ISP 2:

ISP 1

router bgp 1
bgp log-neighbor-changes
network 1.1.1.1 mask 255.255.255.255
network 192.168.1.0
neighbor 192.168.1.2 remote-as 2
neighbor 192.168.1.2 default-originate
neighbor 192.168.1.2 soft-reconfiguration inbound

ISP 2

router bgp 2
bgp log-neighbor-changes
network 2.2.2.2 mask 255.255.255.255
network 192.168.1.0
neighbor 192.168.1.1 remote-as 1
neighbor 192.168.1.1 soft-reconfiguration inbound

R2#sh ip bgp neighbors 192.168.1.1 received-routes
BGP table version is 9, local router ID is 2.2.2.2
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,
x best-external, a additional-path, c RIB-compressed,
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found

Network Next Hop Metric LocPrf Weight Path
*> 0.0.0.0 192.168.1.1 0 1 i
*> 1.1.1.1/32 192.168.1.1 0 0 1 i
* 192.168.1.0 192.168.1.1 0 0 1 i

Total number of prefixes 3

R1

router bgp 3
bgp log-neighbor-changes
network 3.3.3.3 mask 255.255.255.255
network 192.168.2.0
neighbor 192.168.2.1 remote-as 2
neighbor 192.168.2.1 soft-reconfiguration inbound

R3#sh ip bgp neighbors 192.168.2.1 received-routes
BGP table version is 7, local router ID is 3.3.3.3
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,
x best-external, a additional-path, c RIB-compressed,
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found

Network Next Hop Metric LocPrf Weight Path
*> 0.0.0.0 192.168.2.1 0 2 1 i
*> 1.1.1.1/32 192.168.2.1 0 2 1 i
*> 2.2.2.2/32 192.168.2.1 0 0 2 i
*> 192.168.1.0 192.168.2.1 0 0 2 i
* 192.168.2.0 192.168.2.1 0 0 2 i

Total number of prefixes 5

[petercinvest]

Thanks for your reply. I want R1 to receive only 0.0.0.0 B* route, can we use route-map to achieve it and how to?

R2 is further connected to R1 using ebgp, so this 0..0.0.0 will also go to R2's routing table, right?

[Georg Pauwen]

Use a prefix list on R1 and apply it to the BGP neighbor on ISP 2:

R1#conf t

R1(config)#ip prefix list DEFAULT_ONLY permit 0.0.0.0/0

R1(config)#router bgp x

R1(config-router)#neighbor x.x.x.x prefix-list DEFAULT_ONLY in

Any neighbor connected downstream from R1 will also only receive the default route, that is correct, in addition to any networks locally originated on R1.

[petercinvest]

thanks, I use different approach, I use prefix to match 0.0.0.0, then redistribute to EIGRP, so all my IGP neighbor R2, R3 recieve default DEX route 0.0.0.0, if using your approach, R2 and R3 will receive a B* 0.0.0.0 route, so which solution is better, can you share your opinion.

my objective is my IGP R2, R3 get default route from ISP