12-06-2016 05:40 AM - edited 03-08-2019 08:27 AM
Hi guys, As far as I know if a router learns a specific route from different routing protocol then it will prefer routes in this sequence eBGP > EIGRP > OSPF > IS-IS > RIP > iBGP. But in my nexus 7k I saw my router is learning routes 10.1.36.0/24 & 10.1.37.0/24 from eBGP as well as from OSPF. But when I see routing table it shows OSPF routes rather eBGP. Can anyone explain why it is happening. Below is FYI.
test# show ip bgp neighbors 172.18.162.81 routes vrf GTR
Network Next Hop Metric LocPrf Weight Path
* e10.1.36.0/24 172.18.162.81 0 4828 ?
* e10.1.37.0/24 172.18.162.81 0 4828 ?
*>e10.1.38.0/24 172.18.162.81 0 4828 10081 ?
test# show ip route vrf GTR | sec 10.1.3
10.1.36.0/24, ubest/mbest: 1/0
*via 172.18.162.170, Eth2/2.809, [110/1], 6w6d, ospf-1, type-2, tag 4828
10.1.37.0/24, ubest/mbest: 1/0
*via 172.18.162.170, Eth2/2.809, [110/1], 6w6d, ospf-1, type-2, tag 4828
10.1.38.0/24, ubest/mbest: 1/0
*via 172.18.162.81, [20/0], 3w2d, bgp-64511, external, tag 4828
10.1.39.0/24, ubest/mbest: 1/0
*via 172.18.162.170, Eth2/2.809, [110/1], 6w6d, ospf-1, type-2, tag 4828
12-06-2016 07:58 AM
Would you post the BGP configuration and the OSPF configuration? Also information about the VRFs configured on the router?
HTH
Rick
12-06-2016 11:50 PM
Hi Burts, Thanks for your reply. Please have required configurations below as you asked. Please let me know if you need any other further information.
test# show running-config vrf GTR
vrf context GTR
router ospf 1
vrf GTR
default-information originate
redistribute bgp 64511 route-map Perm-Routes
router bgp 64511
vrf GTR
router-id 172.18.255.135
address-family ipv4 unicast
redistribute ospf 1 route-map Perm-Routes
neighbor 172.18.162.81 remote-as 4828
address-family ipv4 unicast
interface Ethernet2/2.809
vrf member GTR
ip address 172.18.162.169/30
ip router ospf 1 area 0.0.0.0
interface Ethernet2/6.1104
vrf member GTR
ip address 172.18.162.82/30
interface Ethernet10/1.1104
vrf member GTR
test# show route-map Perm-Routes
route-map Perm-Routes, permit, sequence 10
Match clauses:
Set clauses:
12-07-2016 07:48 AM
Thank you for the requested information. It does show that both BGP and OSPF are running in the VRF and that eliminates a potential source of the problem which might have been that one protocol was learning routes in a different VRF.
Would you post the output of show ip bgp and of show ip route
HTH
Rick
12-07-2016 09:52 AM
Hi Burts, Thanks again for your reply. Please find your requested information below. Please feel free to ask if you need any further information.
show ip bgp
======================
Test# show ip bgp vrf GTR
BGP routing table information for VRF GTR, address family IPv4 Unicast
BGP table version is 2816, local router ID is 172.18.255.135
Status: s-suppressed, x-deleted, S-stale, d-dampened, h-history, *-valid, >-best
Path type: i-internal, e-external, c-confed, l-local, a-aggregate, r-redist
Origin codes: i - IGP, e - EGP, ? - incomplete, | - multipath
Network Next Hop Metric LocPrf Weight Path
*>r10.1.36.0/24 0.0.0.0 1 100 32768 ?
* e 172.18.162.81 0 4828?
*>r10.1.37.0/24 0.0.0.0 1 100 32768 ?
* e 172.18.162.81 0 4828?
*>e10.1.38.0/24 172.18.162.81 0 48281008
1 ?
*>r10.1.39.0/24 0.0.0.0 1 100 32768 ?
*>r10.33.36.0/27 0.0.0.0 1 100 32768 ?
* e 172.18.162.81 0 48286500
1 ?
*>r10.33.36.32/27 0.0.0.0 1 100 32768 ?
* e 172.18.162.81 0 48286500
1 ?
*>r10.33.46.0/27 0.0.0.0 1 100 32768 ?
*>r10.33.46.32/27 0.0.0.0 1 100 32768 ?
*>r172.16.62.112/28 0.0.0.0 20 100 32768 ?
*>r172.16.63.112/28 0.0.0.0 20 100 32768 ?
*>r172.18.115.112/28 0.0.0.0 1 100 32768 ?
*>r172.18.116.112/28 0.0.0.0 1 100 32768 ?
*>r172.18.162.172/30 0.0.0.0 48 100 32768 ?
*>r172.18.164.0/29 0.0.0.0 1 100 32768 ?
*>r172.18.164.8/29 0.0.0.0 1 100 32768 ?
*>r172.18.164.16/29 0.0.0.0 1 100 32768 ?
*>r172.18.164.24/29 0.0.0.0 1 100 32768 ?
*>r172.29.6.0/29 0.0.0.0 44 100 32768 ?
*>r172.29.6.8/29 0.0.0.0 44 100 32768 ?
*>r172.29.6.16/29 0.0.0.0 44 100 32768 ?
*>r172.29.6.24/29 0.0.0.0 44 100 32768 ?
Test#
Show ip ospf
======================
Test# show ip route vrf GTR
IP Route Table for VRF "GTR"
10.1.36.0/24, ubest/mbest: 1/0
*via 172.18.162.170, Eth2/2.809, [110/1], 7w0d, ospf-1, type-2, tag 4828
10.1.37.0/24, ubest/mbest: 1/0
*via 172.18.162.170, Eth2/2.809, [110/1], 7w0d, ospf-1, type-2, tag 4828
10.1.38.0/24, ubest/mbest: 1/0
*via 172.18.162.81, [20/0], 3w4d, bgp-64511, external, tag 4828
10.1.39.0/24, ubest/mbest: 1/0
*via 172.18.162.170, Eth2/2.809, [110/1], 7w0d, ospf-1, type-2, tag 4828
10.33.36.0/27, ubest/mbest: 1/0
*via 172.18.162.170, Eth2/2.809, [110/1], 7w0d, ospf-1, type-2, tag 4828
10.33.36.32/27, ubest/mbest: 1/0
*via 172.18.162.170, Eth2/2.809, [110/1], 7w0d, ospf-1, type-2, tag 4828
10.33.46.0/27, ubest/mbest: 1/0
*via 172.18.162.170, Eth2/2.809, [110/1], 7w0d, ospf-1, type-2, tag 4828
10.33.46.32/27, ubest/mbest: 1/0
*via 172.18.162.170, Eth2/2.809, [110/1], 7w0d, ospf-1, type-2, tag 4828
172.16.62.112/28, ubest/mbest: 1/0
*via 172.18.162.170, Eth2/2.809, [110/20], 7w0d, ospf-1, type-2
172.16.63.112/28, ubest/mbest: 1/0
*via 172.18.162.170, Eth2/2.809, [110/20], 7w0d, ospf-1, type-2
172.18.115.112/28, ubest/mbest: 1/0
*via 172.18.162.170, Eth2/2.809, [110/1], 7w0d, ospf-1, type-2, tag 4828
172.18.116.112/28, ubest/mbest: 1/0
*via 172.18.162.170, Eth2/2.809, [110/1], 7w0d, ospf-1, type-2, tag 4828
172.18.162.80/30, ubest/mbest: 1/0, attached
*via 172.18.162.82, Eth2/6.1104, [0/0], 7w0d, direct
172.18.162.82/32, ubest/mbest: 1/0, attached
*via 172.18.162.82, Eth2/6.1104, [0/0], 7w0d, local
172.18.162.168/30, ubest/mbest: 1/0, attached
*via 172.18.162.169, Eth2/2.809, [0/0], 7w0d, direct
172.18.162.169/32, ubest/mbest: 1/0, attached
*via 172.18.162.169, Eth2/2.809, [0/0], 7w0d, local
172.18.162.172/30, ubest/mbest: 1/0
*via 172.18.162.170, Eth2/2.809, [110/48], 7w0d, ospf-1, intra
172.18.164.0/29, ubest/mbest: 1/0
*via 172.18.162.170, Eth2/2.809, [110/1], 7w0d, ospf-1, type-2, tag 4828
172.18.164.8/29, ubest/mbest: 1/0
*via 172.18.162.170, Eth2/2.809, [110/1], 7w0d, ospf-1, type-2, tag 4828
172.18.164.16/29, ubest/mbest: 1/0
*via 172.18.162.170, Eth2/2.809, [110/1], 7w0d, ospf-1, type-2, tag 4828
172.18.164.24/29, ubest/mbest: 1/0
*via 172.18.162.170, Eth2/2.809, [110/1], 7w0d, ospf-1, type-2, tag 4828
172.29.6.0/29, ubest/mbest: 1/0
*via 172.18.162.170, Eth2/2.809, [110/44], 7w0d, ospf-1, intra
172.29.6.8/29, ubest/mbest: 1/0
*via 172.18.162.170, Eth2/2.809, [110/44], 7w0d, ospf-1, intra
172.29.6.16/29, ubest/mbest: 1/0
*via 172.18.162.170, Eth2/2.809, [110/44], 7w0d, ospf-1, intra
172.29.6.24/29, ubest/mbest: 1/0
*via 172.18.162.170, Eth2/2.809, [110/44], 7w0d, ospf-1, intra
Test#
12-07-2016 11:17 PM
Hi Burts,
Thanks for your effort to help me.
Please be informed that I guess I got my answer from another discussion in the forum. I guess following things happened here. Please comment if you have any dispute regarding below points.
============================================
Normally the issue you are seeing is -
1) the BGP route received has an AD of 20 and the OPSF route has an AD of 110. So the BGP route is installed into the IP routing table.
An EBGP learned route has a BGP weight of 0
2) the EBGP link goes down. The OSPF route is now installed into the routing table and redistributed into BGP. So that route is now also in the BGP table.
A redistributed route is considered locally generated by BGP and so gets a weight of 32768
3) the EBGP link comes back up and so now the router has to two entries for the same network in it's BGP table. So using the best path selection BGP chooses the one with the higher weight and so sticks with the route learnt from OSPF.
The usual way around this is to simply modify the weight of all EBGP learnt routes to be higher than the locally generated route weight.
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