mailing list archives
Re: Please help our simple bgp
From: Jimmy Hess <mysidia () gmail com>
Date: Sat, 4 Feb 2012 10:51:25 -0600
On Mon, Jan 30, 2012 at 8:27 PM, Ann Kwok <annkwok80 () gmail com> wrote:
We discover the routes is going to ISP A only even the bandwidth 100M is
Can we set the weight to change to ISP B to use ISP B as preference routes?
Can the following configuration work?
Tuning weights and localpreference values can influence traffic that your
equipment sends _to_ ISP A and ISP B. These options do not control what
incoming traffic gets forwarded into your network _from_ ISP A or ISP
B; you need a separate strategy for incoming bits.
The config you listed should do just what the vendor documentation says it
does, so I can't say it doesn't "work"; it just does nothing to help
remedy the situation.
That is, if you have two ISP links each 100M full duplex; and one of them
is at 100% outbound usage, increasing the weight of all the other
neighbor's paths assuming the set of prefixes received over BGP are the
same, will mean that ISP B is the preferred next-hop for each path;
which means ISP A outgoing utilization should drop to near 0, and then
ISP B should be just as fully utilized as ISP A is currently.
You could instead identify some specific paths that are heavy users or
would carry a high percentage of the outgoing traffic, and use
filters/route maps to adjust local preference of specific paths, to
take outgoing load off ISP A.
or increase the weight for 188.8.131.52/1 on routes received from ISP B,
and allow your outgoing traffic to rest of the address space to utilize
ISP A, for example.
But the preferred fix for this problem would be to upgrade ISP A and ISP B
links to at least double their current capacity.
Weight is a vendor-specific parameter, local to your router. I would
consider increasing the default local preference for ISP A first, by the
But as long as you only have one router on which ISP A and ISP B sessions
when you have an identical prefix from ISP A and B, the outgoing path
ISP B is to be preferred by your local router, if the path has a higher
" What suggest to this weight no. too? "
With weights the magnitude of the numbers and the numerical difference
between weights is not significant; it just matters if one path has a
higher weight, or both paths have equal weight.
I would suggest weights that are uniformly spaced apart and easy to
remember, e.g. 100 200 300 400. When you want to add ISP C later, you
will also have flexibility without re-assigning your existing weights.
If this works, how is ISP B upstream connection is down?
Can it still be failover to ISP A automatically?
If it won't work, Do you have any suggestion?
Thank you for your help