Re: Slightly OT: PfARGHHHHHHHH!

Which carries block prepend?

Sent from handheld

On Aug 20, 2012, at 8:37 PM, "marc edwards" <renorider_at_gmail.com> wrote:

> That is exactly what I was looking for! Much appreciated.
>
> Regards,
>
> Marc
>
> On Mon, Aug 20, 2012 at 5:17 PM, Joe Sanchez <marco207p_at_gmail.com> wrote:
>
>> 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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>>>
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>
>
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Received on Tue Aug 21 2012 - 00:39:34 ART