09-17-2008 09:52 AM - edited 03-03-2019 11:35 PM
Hi Guys
Scenerio is
(AS100) (AS100) (AS200)
R4----------R1------------------R2
IBGP EBGP
On R4 (L0 4.4.4.4/32 & L1 44.44.44.44/32) I applied Community no-export and send community to R1
R1 received both the routes
On R1 I applied community none and used access list to permit 4.4.4.4 to advertise it to R2
ITs not happening....
As per Jeff Doyle (Routing TCP/IP ) on page 272 it should happen
Solved! Go to Solution.
09-18-2008 05:17 AM
Hello Anand,
try to give a look at the following:
http://www.cisco.com/en/US/tech/tk365/technologies_configuration_example09186a00801475b2.shtml
Hope to help
Giuseppe
09-17-2008 11:35 AM
Don't have Doyle's book at hand. What's not happening, R2 isn't seeing 4.4.4.4?
Do you have send-community configured on R1's EBGP peer to R2?
PS:
Not too long ago, I ran into an issue where no-exports were being exported because send-community not configured. In other words, correct community processing appear to depend on send-community be configured with peer.
09-17-2008 11:55 AM
Hello Anand,
you need to use an inbound route-map on R1 in order to remove the no-export community early enough to allow R1 to send the prefix.
If the prefix is accepted on R1 with community no-export it will not advertise it
post your config to get better help
Hope to help
Giuseppe
09-17-2008 07:14 PM
R4 config:
R4#show run | b r b
router bgp 100
no synchronization
bgp log-neighbor-changes
network 4.4.4.4 mask 255.255.255.255
network 44.44.44.44 mask 255.255.255.255
neighbor 14.1.1.1 remote-as 100
neighbor 14.1.1.1 send-community
neighbor 14.1.1.1 route-map bbc out
no auto-summary
!
ip classless
no ip http server
!
ip prefix-list 1 seq 5 permit 4.4.4.4/32
!
route-map bbc permit 10
match ip address prefix-list 1
set community no-export
!
route-map bbc permit 20
R1 Config:
R1#show run | b r b
router bgp 100
no synchronization
bgp log-neighbor-changes
network 1.1.1.1 mask 255.255.255.255
neighbor 12.1.1.2 remote-as 200
neighbor 12.1.1.2 next-hop-self
neighbor 12.1.1.2 send-community
neighbor 12.1.1.2 route-map bbc out
neighbor 13.1.1.3 remote-as 300
neighbor 14.1.1.4 remote-as 100
no auto-summary
!
ip classless
no ip http server
!
ip prefix-list 10 seq 5 permit 4.4.4.4/32
!
route-map bbc permit 10
match ip address prefix-list 10
set community none
!
route-map bbc permit 20
09-17-2008 11:52 PM
Hello,
You need an "neighor R2 route-map bbc in"
to be able to remove the no-export community.
Just curious exactly what you are trying to achieve. Is this a real scenario , or are you just studying the use of these communities?
Regards,
Vlad
09-18-2008 12:08 AM
I did that but the Problem is R1 not advertising the 4.4.4.4 route to R2
R1#show ip bgp neighbors 12.1.1.2 advertised-routes
BGP table version is 5, local router ID is 1.1.1.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*> 1.1.1.1/32 0.0.0.0 0 32768 i
*>i44.44.44.44/32 14.1.1.4 0 100 0 i
09-18-2008 12:22 AM
On R4 you are advertising the network with the no-export community.
On R1 you need to remove the no-export on the route as you learn it inbound from R4 in order to advertise it on.
You are trying to alter the route as it goes out to R2. but as the route will not be advertised to R2 because of the no-export you can not alter it outbound.
Remove the no-export from the routes as you learn them and they will be advertised.
HTH
Steve
09-18-2008 12:28 AM
I understand what u said Steve but how in Jeff doyle (TCP/IP vol2) gave this example.
And u know if I add community none At R1 interface(connected to R4) the route comes but in that situation there is no value of using the community
09-18-2008 03:31 AM
Hello Anand,
BGP communities are very useful as a way to mark groups of routes in order to give to iBGP neighbors and eBGP peers an abstract criteria for performing some route manipulation:
for example suppose provider A is a client of provider B
provider A offers two internet access services : a basic free access and a premium services.
provider A and provider B agree that provider A will send routes of free service as 1000:1010 and routes for premium services as 1000:2020. Provider B will use this info to provide a different treatment to the two groups of routes.
Without using community every time a change is made in the usage and distribution of subnets to service mapping both provider A and provider B need to change their configs.
By using the BGP community only provider A makes changes like moving a subnet from a service to the other or adding a new subnet: provider B working on BGP community doesn't need to make any change the new/moved IP subnet will be advertised with the appropriate BGP community and treated accordingly by provider B.
In your scenario you can understand that BGP has different tables: one for the received BGP advertisements, one for policies, and one for the BGP prefixes to be advertised : without using a inbound route-map on R1 the BGP community no-export will exclude the prefix from the outgoing table and so when you try to remove the community is too late
Hope to help
Giuseppe
09-18-2008 03:56 AM
Guys I am still confused can u provide me some good link to clear the Community fundamentals
09-18-2008 05:17 AM
Hello Anand,
try to give a look at the following:
http://www.cisco.com/en/US/tech/tk365/technologies_configuration_example09186a00801475b2.shtml
Hope to help
Giuseppe
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