ASR 1002 X Donnot Redistributed recieved BGp routes

[admin@atrinnet.net]

Hi router A announce prefix x.x.x.x/y to routerB on IBGP

router B IS asr1002X by donnot redistruited prefix    x.x.x.x/y To uplink internet bgp session

Router is exsited in routing table router A by IBGp distance 200

uplink internet advertise routes limit by prefix-list and in prefix-list x.x.x.x/y exsited

How solve this  ????

any idea?

[MHM Cisco World]

MHM 

[admin@atrinnet.net]

For ebgp under router a uplink is router A

whitch command need B that redistribued Router B prefix on internet uplink ???

[MHM Cisco World]

MHM

[Giuseppe Larosa]

Hello admin@atrinnet.net ,

check all the BGP attributes attached to the prefix x.x.x.x/y using

show ip bgp x.x.x.x/y

on RouterB

look at the BGP communities values attached to it if you see the well known BGP community no-export or NO-EXPORT this a possible reason why RouterB does not advertise the prefix to ISP.

no-export BGP community allows a prefix to be propagated within an AS in iBGP but it does not allow to advertise it to an eBGP peer.

the BGP next-hop cannot be an issue by default BGP next-hop is rewritten over an eBGP session using the IP address used to talk with  the eBGP peer.

Hope to help

Giuseppe

[admin@atrinnet.net]

the community is none

show ip bgp x.x.x.x/y
BGP routing table entry for x.x.x.x/y, version 22811
Paths: (1 available, best #1, table default)
Not advertised to any peer
Refresh Epoch 1
208555 51026, (received & used)
172.18.22.22 from 172.18.22.22 (185.217.6.50)
Origin IGP, localpref 100, valid, internal, best
rx pathid: 0, tx pathid: 0x0
Updated on Aug 19 2024 14:58:34 UTC

show in bgp no advetise to any peers

now

show ip bgp neighbors 172.18.14.253 advertised-routes

Total number of prefixes 0

172.18.14.253 is uplink router B

[Harold Ritter]

Hi admin@atrinnet.net ,

The "Not advertised to any peer" leads me to believe that the prefix list does not really allow this specific prefix. Can you do a "show bgp ipv4 unicast <prefix-list name>" on router B and see if the command returns the specific prefix.

Regards,

[admin@atrinnet.net]

Hi Dears

Bgp neighbor limitation

address-family ipv4
bgp redistribute-internal
neighbor 172.18.14.253 activate
neighbor 172.18.14.253 route-map edge out

route-map section :

show route-map edge
route-map edge, permit, sequence 1
Match clauses:
ip address prefix-lists: mobin
Set clauses:
Policy routing matches: 0 packets, 0 bytes

prefix include

show ip prefix-list mobin
ip prefix-list mobin: 2 entries
seq 5 permit 45.129.36.0/24 le 32
seq 1000 deny 0.0.0.0/0 le 32

show ip bgp neighbors 172.18.14.253 advertised-routes

Total number of prefixes 0

show ip bgp 45.129.36.0/24
BGP routing table entry for 45.129.36.0/24, version 22811
Paths: (1 available, best #1, table default)
Not advertised to any peer
Refresh Epoch 1
208555 51026, (received & used)
172.18.22.22 from 172.18.22.22 (185.217.6.50)
Origin IGP, localpref 100, valid, internal, best
rx pathid: 0, tx pathid: 0x0
Updated on Aug 19 2024 14:58:34 UTC

[Giuseppe Larosa]

Hello admin@atrinnet.net ,

rewrite the prefix-list in the following manner:

no seq 5 permit 45.129.36.0/24 le 32

seq 5 permit 45.129.36.0/24

without adding the le 32 the prefix-list will look for an exact match with your prefix. The current statement looks for prefixes that are within 45.129.36.0/24 but the prefix itself is not a match.

Hope to help

Giuseppe

[Harold Ritter]

Hi Giuseppe,

>seq 5 permit 45.129.36.0/24 le 32

This prefix list entry should be fine and will definitely permit 45.129.36.0/24.

Regards,

Regards,

[Giuseppe Larosa]

Hello @Harold Ritter ,

yes we have been confused by the fact the OP admin@atrinnet.net made us to think of an eBGP session , but it is now clear it is an iBGP session and this explains why RB cannot advertise the prefix to RC for the iBGP split horizon rule.

either he makes a direct iBGP session between RA and RC or it has to configure RB as a route reflector server by adding neighbor x.x.x.x route-reflector-client under BGP or under the correct address family.

Hope to help

Giuseppe

[Harold Ritter]

Hi admin@atrinnet.net ,

Try performing a "clear bgp ipv4 unicast * soft". You should perform this command every time you change your BGP policies.

Regards,

[Giuseppe Larosa]

Hello admin@atrinnet.net ,

ok BGP communities are not an issue here

>>

show ip bgp neighbors 172.18.14.253 advertised-routes

Total number of prefixes 0

at this point I agree with @Harold Ritter verify if the prefix-list allows the prefix or not.

Hope to help

Giuseppe

[paul driver]

Hello
Can you confirm if the "internet" bgp peering is in the same ASN as rtr A/B ?, if so then the route will not be advertised, due to ibgp split horizon initiating --- a received ibgp route will not be readvertised to another ibgp peer

[admin@atrinnet.net]

when used show ip protocols donnot show me any route-maps assign to bgp neigbors

show ip protocols
*** IP Routing is NSF aware ***

Routing Protocol is "application"
Sending updates every 0 seconds
Invalid after 0 seconds, hold down 0, flushed after 0
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
Maximum path: 32
Routing for Networks:
Routing Information Sources:
Gateway Distance Last Update
Distance: (default is 4)

Routing Protocol is "bgp 204203"
Outgoing update filter list for all interfaces is not set
Incoming update filter list for all interfaces is not set
IGP synchronization is disabled
Automatic route summarization is disabled
Neighbor(s):
Address FiltIn FiltOut DistIn DistOut Weight RouteMap
172.18.14.253
172.18.19.13