10-25-2017 07:58 PM - edited 03-05-2019 09:22 AM
We currently have head office and few branches with BGP running for site to site connectivity over the WAN. I am trying to get head around how the default route for bgp works.
Below is a similar configuration of on one of our remote sites.
router bgp 6xx06
bgp router-id 1.1.1.1
bgp log-neighbor-changes
network 1.111.6.111 mask 255.255.255.255
redistribute connected
neighbor 1.1.111.1 remote-as 6xx01
neighbor 1.1.111.1 timers 8 24
neighbor 1.1.111.1 send-community
neighbor 1.1.111.1 soft-reconfiguration inbound
neighbor 1.1.111.1 weight 10
neighbor 1.1.111.1 prefix-list Site-routes-in in
neighbor 1.1.111.1 prefix-list Site-routes-out out
neighbor 1.1.111.1 route-map Site-link-in in
neighbor 1.1.111.1 route-map Site-link-out out
When we look at the - show ip route command below is the brief output from a remote site.
#show ip route
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route, H - NHRP, l - LISP
+ - replicated route, % - next hop override
Gateway of last resort is 1.1.111.1 to network 0.0.0.0
B* 0.0.0.0/0 [20/0] via 1.1.111.1, 4w2d
10.0.0.0/8 is variably subnetted, 66 subnets, 4 masks
B 10.0.0.0/8 [20/0] via 1.1.111.1, 2w2d
B 10.150.0.0/16 [20/0] via 1.1.111.1, 4w2d
B 10.150.0.0/24 [20/0] via 1.1.111.1, 4w2d
B 10.150.1.0/24 [20/0] via 1.1.111.1, 4w2d
B 10.150.2.0/24 [20/0] via 1.1.111.1, 4w2d
B 10.150.3.0/24 [20/0] via 1.1.111.1, 4w2d
My doubt is how did the B* route come into play? How does 0.0.0.0 go via 1.1.111.1?
I checked the full running configuration but could not find out. Can you guys point me in the correct direction? Is this done by ISP?
Solved! Go to Solution.
10-26-2017 04:06 AM
Hello,
headquarters is sending the default route, one way or another. You cannot really tell how, but if you an produce the output of 'show ip bgp neighbors x.x.x.x received-routes', it gives you an indication:
R2#sh ip bgp neighbors 192.168.1.1 received-routes
BGP table version is 6, 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 0 1 i
*> 1.1.1.1/32 192.168.1.1 0 0 1 i
* 192.168.1.0/30 192.168.1.1 0 0 1 i
The 'i' at the end means the default route is either sent with the 'network 0.0.0.0' command, or the 'neighbor x.x.x.x default-originate' command/
If you see a '?' instead of the 'i' in the Path field, that means the default route is sent by means of the 'default-information originate' command under the BGP process...
10-25-2017 08:07 PM
Hi,
@jeetkulkarni wrote:
We currently have head office and few branches with BGP running for site to site connectivity over the WAN. I am trying to get head around how the default route for bgp works.
Below is a similar configuration of on one of our remote sites.
router bgp 6xx06
bgp router-id 1.1.1.1
bgp log-neighbor-changes
network 1.111.6.111 mask 255.255.255.255
redistribute connected
neighbor 1.1.111.1 remote-as 6xx01
neighbor 1.1.111.1 timers 8 24
neighbor 1.1.111.1 send-community
neighbor 1.1.111.1 soft-reconfiguration inbound
neighbor 1.1.111.1 weight 10
neighbor 1.1.111.1 prefix-list Site-routes-in in
neighbor 1.1.111.1 prefix-list Site-routes-out out
neighbor 1.1.111.1 route-map Site-link-in in
neighbor 1.1.111.1 route-map Site-link-out out
When we look at the - show ip route command below is the brief output from a remote site.
#show ip route
Gateway of last resort is 1.1.111.1 to network 0.0.0.0
B* 0.0.0.0/0 [20/0] via 1.1.111.1, 4w2d
10.0.0.0/8 is variably subnetted, 66 subnets, 4 masks
My doubt is how did the B* route come into play? How does 0.0.0.0 go via 1.1.111.1?
I checked the full running configuration but could not find out. Can you guys point me in the correct direction? Is this done by ISP?
It is advertised from the neighbor. Please share the output of 'sh run | s route-map|prefix-list. It could be found in the accepted routes configuration.
HTH,
Meheretab
10-26-2017 01:23 AM
Hello,
in addition to Meheretab's post, post the full BGP configuration of the head office router. Look for any of the lines in bold (your IP addresses are different, obviously)...
router bgp 1
bgp log-neighbor-changes
network 1.1.1.1 mask 255.255.255.255
network 192.168.1.0 mask 255.255.255.252
network 0.0.0.0
redistribute static
neighbor 192.168.1.2 remote-as 2
neighbor 192.168.1.2 default-originate
default-information originate
ip route 0.0.0.0 0.0.0.0 192.168.1.1
10-26-2017 02:48 AM
I cannot paste full configuration as of now but i found that the head office routes had this prefix entry. Probably that's the reason i think
ip prefix-list HO-routes-in description "Permit routes from HeadOffice"
ip prefix-list HO-routes-in seq 100 permit 192.168.0.0/16 ge 32
ip prefix-list HO-routes-in seq 110 permit 10.150.0.0/16
ip prefix-list HO-routes-in seq 120 permit 0.0.0.0/0 ??
10-26-2017 04:06 AM
Hello,
headquarters is sending the default route, one way or another. You cannot really tell how, but if you an produce the output of 'show ip bgp neighbors x.x.x.x received-routes', it gives you an indication:
R2#sh ip bgp neighbors 192.168.1.1 received-routes
BGP table version is 6, 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 0 1 i
*> 1.1.1.1/32 192.168.1.1 0 0 1 i
* 192.168.1.0/30 192.168.1.1 0 0 1 i
The 'i' at the end means the default route is either sent with the 'network 0.0.0.0' command, or the 'neighbor x.x.x.x default-originate' command/
If you see a '?' instead of the 'i' in the Path field, that means the default route is sent by means of the 'default-information originate' command under the BGP process...
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