[Xorp-users] BGP conditional route advertising

[Robert Bays]

Mihai,

If your CIDR block is large enough (/23 or greater) split your supernet 
into two subnets.  Announce the supernet out your backup link and the 
subnets out your primary link.  Most, if not all, traffic will flow 
inbound through your primary link based on longest prefix match.

Cheers,
Robert.

mihai at duras.ro wrote:
> 1. I don't know if I'm that good with coding in regard to Xorp but I'll
> give it a try.
> 
> 2. I was taking about the following case:
> 
> Provider --.> Upstream 1 ISP  --> Telia
> 
> same Provider --> Upstream 2 ISP --> Level-3 let's say
> 
> Telia will always return traffic to you via Upstream 1 ISP...but let's say
> you'd like to use one link for all traffic (download and upload) and the
> other one only as backup (financial reasons)
> 
> That was what I was pointing at:)
> 
> 3. Thought about the script option..but I was looking more at something
> built-in...looks like I'll have to document myself and add it to the
> existing code.
> 
> 
>> On Fri, Sep 01, 2006 at 11:56:21AM +0300, mihai at duras.ro wrote:
>>> I'll try adding a feature request then.
>>>
>>> Prepending is sometimes not enough.
>>>
>>> For example some upstream providers will always place a higher weight,
>>> local pref,etc on a route received from a certain peer and thus render
>>> the
>>> as-path prepend unusable.
>> Certainly. I'd say just about everyone places a
>> higher local preference on their own customers,
>> but that lpref won't be visible beyond your
>> upstream so just about everyone else on the
>> Internet will choose the best route based on the
>> shortest AS-PATH.
>>> What I want is:
>>>
>>> Announce my route over ISP1 while ISP1 is online (and don't receive any
>>> traffic on the backup ISPs).
>>> If ISP1 down then announce via ISP2.
>>> If ISP2 down..and so on.
>> You could probably do this via some form of shell
>> script that polls to see if ISP1 is down or not
>> and then add an advertisement via ISP2.
>> or buy a Cisco.. or do some XORP coding :)
>>
>> Regards,
>>    Kristian.
>>
>>
>>>> On Fri, Sep 01, 2006 at 11:25:01AM +0300, mihai at duras.ro wrote:
>>>>> Hello,
>>>>>
>>>>> Sorry if this has been asked before but I had no luck while
>>> google-ing
>>>>> for
>>>>> it.
>>>>>
>>>>> Does XORP support BGP conditional route advertising as Cisco does
>>> with
>>>>> the
>>>>> advertise map per-neighbor command ?
>>>> As far as I know it does not, but it would indeed
>>>> be a nice feature. You could add a feature request
>>>> at http://www.xorp.org/bugzilla/index.cgi with a
>>>> small description of what you want :)
>>>>
>>>>> I'm searching for a solution to advertise some prefixes on a backup
>>> link
>>>>> only if the main link goes down (the default gateway is no longer
>>>>> received
>>>>> on it with an AS-PATH of the neighbors AS)
>>>> Isn't prepending your as-path enough?
>>>>
>>>> Regards,
>>>>     Kristian.
>>>>
>>>> --
>>>> Kristian Larsson                                   KLL-RIPE
>>>> Network Engineer                      Net at Once [AS35706]
>>>> +46 704 910401			     kristian at spritelink.se
>>>>
>>>
> 
> 
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