Re: Slightly OT: PfARGHHHHHHHH!

Marc, does this help:

   - BGP Autonomous System Number Community Prepend

  When an entrance link goes out-of-policy (OOP) due to delay, or in images
prior to Cisco IOS Releases 15.2(1)T1 and 15.1(2)S, and PfR selects a best
entrance for an inside prefix, a BGP prepend community is attached one at a
time (up to a maximum of six) to the inside prefix BGP advertisement from
the network to another autonomous system such as an ISP. In Cisco IOS
Releases 15.2(1)T1, 15.1(2)S, and later releases, when an entrance link
goes out-of-policy (OOP) due to unreachable or loss reasons, and PfR
selects a best entrance for an inside prefix, six BGP prepend communities
are attached to the inside prefix BGP advertisement. The BGP prepend
community will increase the number of autonomous system hops in the
advertisement of the inside prefix from the ISP to its peers. Autonomous
system prepend BGP community is the preferred method to be used for PfR BGP
inbound optimization because there is no risk of the local ISP filtering
the extra autonomous system hops. There are some issues, for example, not
all ISPs support the BGP prepend community, ISP policies may ignore or
modify the autonomous system hops, and a transit ISP may filter the
autonomous system path. If you use this method of inbound optimization and
a change is made to an autonomous system, you must issue an outbound
reconfiguration using the clear ip bgp command. The prepend community has
to be configured per Border Router and per external interfaces because the
community value is specific per Service Provider.

Configuration Sample:

!
pfr master
 border 10.4.5.6 key-chain pfr
  interface Ethernet0/1 external
   downgrade bgp community aa:nn (community number in aa:nn format)
  interface Ethernet0/0 internal
!

In this solution guide, PfR will enforce the path by using BGP AS-PATH
prepend for controlled prefixes. PfR will not try to control an inside
prefix unless there is an exact match in the BGP routing information base
(RIB) because PfR does not advertise a new prefix to the Internet.
Joe Sanchez,
Chicago, IL

On Mon, Aug 20, 2012 at 6:45 PM, marc edwards <renorider_at_gmail.com> wrote:

> So what is this half baked product my SE sold me? The documentation looks
> good on Cisco's site and reads
>
> To enforce an entrance link selection, PfR offers the following methods:
> BGP Autonomous System Number Prepend
>
> After PfR selects a best entrance for an inside prefix, extra autonomous
> system hops (up to a maximum of six) are prepended to the inside prefix BGP
> advertisement over the other entrances. The extra autonomous system hops on
> the other entrances increase the probability that the best entrance will be
> used for the inside prefix. This is the default method PfR uses to control
> an inside prefix, and no user configuration is required.
> BGP Autonomous System Number Community Prepend
>
> After PfR selects a best entrance for an inside prefix, a BGP prepend
> community is attached to the inside prefix BGP advertisement from the
> network to another autonomous system such as an ISP. The BGP prepend
> community will increase the number of autonomous system hops in the
> advertisement of the inside prefix from the ISP to its peers. Autonomous
> system prepend BGP community is the preferred method to be used for PfR BGP
> inbound optimization because there is no risk of the local ISP filtering
> the extra autonomous system hops. There are some issues, for example, not
> all ISPs support the BGP prepend community, ISP policies may ignore or
> modify the autonomous system hops, and a transit ISP may filter the
> autonomous system path. If you use this method of inbound optimization and
> a change is made to an autonomous system, you must issue an outbound
> reconfiguration using the clear ip bgp command.
>
>
>
> http://www.cisco.com/en/US/docs/ios-xml/ios/pfr/configuration/15-1mt/pfr-bgp-inbound.html#GUID-52E6BAC0-FE00-43DD-BE37-822FC2ED5C0F
>
>
> This sounds great until I read further and find no configuration references
> to make this happen. Looking through all commands in
>
> http://www.cisco.com/en/US/docs/ios-xml/ios/pfr/command/pfr-cr-book.html
>
> I don't see anything either.
>
>
> Is this blatant false advertising or am I missing something?
>
>
> Regards,
>
> Marc
>
>
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Received on Mon Aug 20 2012 - 19:17:21 ART