OSPF vs IS-IS vs PrivateAS eBGP

Steve Bertrand steve at ibctech.ca
Thu Aug 20 20:22:48 CDT 2009

Gary T. Giesen wrote:
> FWIW, we use BGP to our multihomed customers (even when we manage the
> CPE), using a private AS. OSPF doesn't have the right toolset to
> provide protection for inter-network route propogation, and the risk
> of some customer's CPE screwing up you routing is just too high to go
> naked. A basic CPE BGP config is not too difficult to template, and
> you don't necessarily have to use prefix filters on it (although you
> definitely need them on YOUR) side. And once you've got it deployed,
> you'll find the knobs you can turn to do things like TE (ie. data down
> one pipe, voice down the other, and failover for both) will have both
> you and your customers loving it. (What? I can actually use that spare
> circuit that normally does nothing?!?).

This is pretty much how I do it for our 100Mb fibre clients.

Most of them are upgrading from a <2Mbps SDSL circuit (which has been
hugely profitable) to 100Mb Ethernet over fibre.

Instead of erasing the revenue of the SDSL, I had this bold approach
(mgmt speak) whereas I'd make both circuits worthwhile, by making them

Configure eBGP from your edge to the client edge using private-AS. Since
I already have copy/paste templates (thanks to RANCID), I make it a
habit to ensure filters are at both ends. Goes without saying that
BCP-38 is followed, and strict is deployed everywhere possible.

peer-group and regexes are handy.

Even for clients who have a single connection (particularly where we
control the CPE), I implement eBGP on it so that if I so have the need,
I can move their connection about my network with relative ease, even if
I know they will never be multi-homed into us.

Since my upstream doesn't allow me to BGP peer with them (v4) (they
statically route my own ARIN block to me), my v4 experience ends within
my own network. *sigh*

Either way, even though I'm small and perhaps irrelevant, if in the same
sentence you read "my network" and "customer network", use BGP.

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