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Community Member

BGP received-only Question

Hi

From what I understand in the show ip bgp x.x.x.x/x output the received-only would be present when soft-reconfiguration inbound is configured and the route has been rejected by a policy i.e. a route map

What i have also found is that on many outputs i can see the exact same route in the output twice, one which has the received-only keyword and one doesn't.

Now for a specified neighbor we have a route map configured inbound which will change the weight based on the community value. It seems as though when a route map is configured and an attribute is changed that route appears in the output twice, one being modified and one which is unchanged. But this contradicts what is said on the Cisco website its states 'the received-only keyword will only show up if the route is denied by a policy', but its not.. it's just changed.

Has anyone had this discussion before? I would like to hear people's thoughts on the matter.

Thanks

Andre

corerouter#show ip bgp | b 10.141.54.0

* 10.141.54.0/23 10.199.10.18 0 64000 34406 65502 ?

*> 10.199.10.18 0 64000 34406 65502 ?

corerouter#sho ip bgp 10.141.54.0/23

BGP routing table entry for 10.141.54.0/23, version 1219279

Paths: (4 available, best #3, table Default-IP-Routing-Table)

Advertised to update-groups:

2 3 4 5 6 7

34406 65502

10.199.10.18 from 10.199.10.20 (82.196.60.60)

Origin incomplete, metric 0, localpref 100, weight 64000, valid, external

Community: 10199111

34406 65502, (received-only)

10.199.10.18 from 10.199.10.20 (82.196.60.60)

Origin incomplete, metric 0, localpref 100, valid, external

Community: 10199111

34406 65502

10.199.10.18 from 10.199.10.19 (82.196.60.1)

Origin incomplete, metric 0, localpref 100, weight 64000, valid, external, best

Community: 10199111

34406 65502, (received-only)

10.199.10.18 from 10.199.10.19 (82.196.60.1)

Origin incomplete, metric 0, localpref 100, valid, external

Community: 10199111

3 REPLIES

Re: BGP received-only Question

When you configure bgp soft-configuration-inbound, all the updates received from the neighbor will be stored unmodified, regardless of the inbound policy

This might be the reason for the presence of the route.

BTW, did you try clearing the session and see the results

clear ip bgp soft in

Narayan

Community Member

You are seeing both the

show ip bgp neighbor x.x.x.x received-routes

show ip bgp neighbor x.x.x.x routes

sho ip bgp a.b.c.d

 

If you found this page, like I did, while searching for "received-only" - that means that the route has only been received, but not entered in the routing table. This is good if you meant to block that route.  But if that route is actually also installed in the routing table and you meant to block it, check your route-map, specifically your prefix-lists and you will likely find that you have an error with wither the IP address or the CIDR mask, resulting in a non-match condition. The inverse is also true if you intend to allow a route but you only see the "received-only" route, you probably have a typo in your route-map or prefix list.  Below are some examples that might help.

 

Here are some BGP with route-map and prefix-list examples, although the data is not meaningful. 

 

router bgp 1234

  neighbor CARRIER1 peer-group

  neighbor CARRIER1 route-map PROVIDER1-IN in

  neighbor 6.7.8.9 peer group CARRIER1

 

route-map PROVIDER1-IN deny 5

  match ip address prefix-list MyIPs

route-map PROVIDER1-IN permit 10

  match ip address prefix-list GOOG APPL

 

ip prefix-list GOOG seq 5 permit 8.8.8.0/24 le 32

ip prefix-list GOOG seq 10 permit 8.8.4.4/32

 

ip prefix-list APPL seq 5 per 17.142.160.59/32

ip prefix-list APPL seq 10 per 17.178.96.0/24 le 32

 

ip prefix-list MyIPs seq 5 per 1.2.0.0/16 le 24

ip prefix-list MyIPs seq 10 per 2.3.4.0/24 le 32

ip prefix-list MyIPs seq 15 per 4.5.6.7/32

Cisco Employee

This is in no way to

This is in no way to contradict what you are saying but to clarify the soft-reconfiguration allows for the denied routes to be visible.  When you do a "show ip bgp" you are looking at the input policy engine (prior to being given to the IP RIB for best path consideration)  

IPE contains all the routes -> filters unwanted routes -> (BGP-RIB or Local-RIB) makes best path choices only for BGP ---THEN DOES TWO INDEPENDENT OPERATIONS

1. Passes to IP-RIB for consideration  

2. (Loc-RIB) sends info to output Policy Engine 
     (Filters based on output policy)

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