BGP Route Refresh Capability

(Rene Molenaar) #1

This topic is to discuss the following lesson:

(system) #2

Hi Rene,

I really enjoyed the presentation of your book called how to master ccna. This is the kind of presentation im looking for but most of these books out there have too much detail. Do you have a book for CCENT or atleast can you recommend a similar book for CCENT?

Thanks
Holmes

(sutandra C) #3

Your discussion on BGP synchronization is excellent. Really explains the topic. Many Thanks

(Rene Molenaar) #4

Glad to hear that you enjoyed it!

(Navid D) #5

Thank you for this clear demo.

Anything about Enhanced Route Refresh ?
Thanks,

(Rene Molenaar) #6

Hi Navid,

Glad to hear you like it.

I don’t have anything on Enhanced Route Refresh at the moment. I’ll add it to my list, might be nice for the future.

Rene

(XIN W) #7

question:

why we need “R2#clear ip bgp 192.168.12.1 in” here to make R2 sent Route-refresh? it should send automatically if route-refresh is supported and negotiated, thanks

(Rene Molenaar) #8

Hi Xin,

Using the clear ip bgp in command is a nice way to manually request a route refresh from your neighbor.

Once you do this, you can see it in the debug that R2 is requesting R1 for a refresh:

R2#
BGP: 192.168.12.1 sending REFRESH_REQ(5) for afi/safi: 1/1

Rene

(Mohammad Hasanuz Zaman) #9

Hi Rene,

In summary …

HARD RESET : It will tear down TCP session as well as BGP session.Establishing new BGP session, will send Route refresh request to neighbor and learn all prefix again also network interuption will occured.

Soft Reconfiguration : Need More Memory due to store RAW Prefix in seperate table. No network interuption and will not send any Route refresh request.

Route Refresh : This is the most suitable method.No network interuption , no extra memory needed.Just send a Route refresh request.

Please correct me if I am wrong with my understanding .Thx

br/zaman

(Robert G) #10

Hi NL Team,

If using the route refresh option inbound, I assume any filters we have Inbound will be processed before routes are installed in the actual routing table? Is there any reason one would use soft reconfiguration over route refresh apart from it either being supported / not supported on the platform?
Lastly, for route refresh to work do we need the peer router to be able to support this or only our own local router?
Thanks :grin:

(Rene Molenaar) #11

Hello Robert,

That’s right. When you receive a refreshed route, filters are applied and then it gets installed in the BGP table, and in the routing table.

Today, there is no reason to use soft reconfiguration instead of route refresh. Soft reconfiguration was a bit of a workaround so you didn’t have to do a hard reset. Nowadays, all routers support route refresh so there’s no reason not to use it. Both peers need to support this.

Rene

1 Like
(Robert G) #12

Thanks Rene,

Do we have a way of checking if the remote peer supports route refresh by any commands? Or would it be a case of having to ask the Provider of the peer link if their device supports route refresh?
Thanks
Robert

(Rene Molenaar) #13

Hello Robert,

There is a quick way to see the capabilities when you have established a neighbor adjacency:

R1#show ip bgp neighbors | begin capa   
    1 active, is not multisession capable (disabled)
  Neighbor capabilities:
    Route refresh: advertised and received(new)
    Four-octets ASN Capability: advertised and received
    Address family IPv4 Unicast: advertised and received
    Enhanced Refresh Capability: advertised and received
    Multisession Capability: 
    Stateful switchover support enabled: NO for session 1

Rene