[c-nsp] BGP as-path access list question on 1841 routers

Mon Apr 12 12:41:13 EDT 2010

Right, I believe any router running code written within the last 5 years
supports it today. It is very mature at this point.

Leah

From: Kenny Sallee [mailto:kenny.sallee at gmail.com] 
Sent: Saturday, April 10, 2010 10:05 PM
To: Leah Lynch (Contractor)
Cc: Dan Goldberg; cisco-nsp at puck.nether.net
Subject: Re: [c-nsp] BGP as-path access list question on 1841 routers

That depends on if both BGP neighbors support route refresh capability I
think.  Looks like it's negotiated upon BGP neighbor establishment:

001052: *Apr 10 18:32:18.372 PDT: BGP: <ip> OPEN has ROUTE-REFRESH
capability(old) for all address-families

001053: *Apr 10 18:32:18.372 PDT: BGP: <ip> rcvd OPEN w/ optional
parameter type 2 (Capability) len 2

001054: *Apr 10 18:32:18.372 PDT: BGP: <ip> OPEN has CAPABILITY code: 2,
length 0

001055: *Apr 10 18:32:18.372 PDT: BGP: <ip> OPEN has ROUTE-REFRESH
capability(new) for all address-families

001056: *Apr 10 18:32:18.372 PDT: BGP: <ip> rcvd OPEN w/ optional
parameter type 2 (Capability) len 3

Kenny

On Thu, Apr 1, 2010 at 12:11 PM, Leah Lynch (Contractor)
<leah.lynch at clearwire.com> wrote:

Avoid the soft-reconfiguration statement altogether, it is a legacy
command that stores an extra copy of the table. Just use clear ip bgp
in, that will use the route refresh capability without any extra
configuration or memory use.

Leah

-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net

[mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Kenny Sallee
Sent: Thursday, April 01, 2010 12:03 PM
To: Dan Goldberg
Cc: cisco-nsp at puck.nether.net
Subject: Re: [c-nsp] BGP as-path access list question on 1841 routers

You don't need to specify the 'soft-reconfiguration' under the bgp
neighbor
but I believe you still should do a

clear ip bgp nei <ip> soft in|out

or

clear ip bgp nei <ASN> soft in|out

Kenny

On Thu, Apr 1, 2010 at 11:45 AM, Dan Goldberg <dan.goldberg at vgt.net>
wrote:

>
> I left out a detail that may be important:
> This is on an MPLS WAN where I control all the CEs. The PEs are all
> provider controlled.
> The "hubs" I mentioned are just larger CEs with a broader BGP policy
> permitting all my AS numbers. So each routers neighbor is not under my
> control.
>
> Thanks again.
> Dan
>
> -----Original Message-----
> From: cisco-nsp-bounces at puck.nether.net [mailto:
> cisco-nsp-bounces at puck.nether.net] On Behalf Of Dan Goldberg
> Sent: Thursday, April 01, 2010 1:10 PM
> To: cisco-nsp at puck.nether.net
> Subject: [c-nsp] BGP as-path access list question on 1841 routers
>
> Hi there,
> I have what is probably a very simple BGP question which I wanted to
ask.
> The short version is how to refresh/reread an existing BGP as-path
> access-list (with new permits added) without rebooting the router?
>
> The long version:
> I run primarily IOS Version 12.4(15)T9 on 1841s with EBGP configured
> largely as follows. I have roughly 100 sites like this. For the most
part
> all sites have connectivity to 2 "hubs", a NOC and an alternative
(BCP) NOC.
> Tail sites are not supposed to be able to reach each other or even
know
> about each other (through BGP) in most cases. That is what the as-path
> access list provides.
>
> There are some cases where there are groups of ASes that I want to
allow
> BGP to learn about each other. These relationships are built sometimes
> arbitrarily.
>
> <all numbers are faked>
> router bgp 65534
> network blah mask 255.255.255.255
> neighbor www.xxx.yyy.zzz remote-as 65533
>  neighbor www.xxx.yyy.zzz filter-list 1 in
> !
> ip as-path access-list 1 permit 64542
> ip as-path access-list 1 permit 64543
>
> I have found that if I start with the above as-path filter and then
add a
> new permit to the filter as below:
> ip as-path access-list 1 permit 64551
>
> #sho ip bgp neighbors shows:
> Neighbor capabilities:
>    Route refresh: advertised and received(old & new)
>
> The question (finally):
> Can I use a soft restart to re-read the as-path access-list?
> Do I need to add a "neighbor soft-reconfiguration" statement to BGP
first?
> Is there another method to force a reread of the filter-list without
losing
> connectivity to the router?
>
> Thanks I appreciate your feedback.
>
> --
> Dan Goldberg
> <title removed due to other thread>
> Video Gaming Technologies, Inc.
> 434-992-5450
>
>
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