BGP Design question.

PC paul4004 at gmail.com
Wed Jun 22 18:33:35 CDT 2011


Who makes the firewall?

To make this work and be "hitless", your firewall vendor must support
stateful replication of routing protocol data (including OSPF).  For
example, Cisco didn't support this in their ASA product until version 8.4 of
code.

Otherwise, a failover requires OSPF to re-converge -- and quite frankly,
will likely cause some state of confusion on the upstream OSPF peers, loss
of adjacency, and a loss of routing until this occurs.  It's like someone
just swapped a router with the same IP  to the upstream device -- assuming
your active/standby vendor's implementation only presents itself as one
device.

However, once this is succesful your current failover topology should work
fine -- even if it takes some time to failover.

In my opinion though, unless the firewall is serving as "transit" to
downstream routers or other layer 3 elements, and you need to run OSPF to it
(And through it) as a result, it's often just easier to static default route
out from the firewall(s) and redistribute a static route on the upstream
routers for the subnets behind the firewalls.  It also helps ensure
symmetrical traffic flows, which is important for stateful firewalls and can
become moderatly confusing when your firewalls start having many interfaces.




On Wed, Jun 22, 2011 at 4:27 PM, Bret Palsson <bret at getjive.com> wrote:

> Here is my current setup in ASCII art. (Please view in a fixed width font.)
> Below the art I'll write out the setup.
>
>
>     +--------+    +--------+
>     | Peer A |    | Peer A |  <-Many carriers. Using 1 carrier
>     +---+----+    +----+---+    for this scenario.
>         |eBGP          | eBGP
>         |              |
>     +---+----+iBGP+----+---+
>     | Router +----+ Router |  <-Netiron CERs Routers.
>     +-+------+    +------+-+
>       |A   `.P    A.'    |P   <-A/P indicates Active/Passive
>       |      `.  .'      |      link.
>       |        ::        |
>     +-+------+'  `+------+-+
>     |Act. FW |    |Pas. FW |  <-Firewalls Active/Passive.
>     +--------+    +--------+
>
>
> To keep this scenario simple, I'm multihoming to one carrier.
> I have two Netiron CERs. Each have a eBGP connection to the same peer.
> The CERs have an iBGP connection to each other.
> That works all fine and dandy. Feel free to comment, however if you think
> there is a better way to do this.
>
> Here comes the tricky part. I have two firewalls in an Active/Passive
> setup. When one fails the other is configured exactly the same
> and picks up where the other left off. (Yes, all the sessions etc. are
> actively mirrored between the devices)
>
> I am using OSPFv2 between the CERs and the Firewalls. Failover works just
> fine, however when I fail an OSPF link that has the active default route,
> ingress traffic still routes fine and dandy, but egress traffic doesn't.
> Both Netiron's OSPF are setup to advertise they are the default route.
>
> What I'm wondering is, if OSPF is the right solution for this. How do
> others solve this problem?
>
>
> Thanks,
>
> Bret
>
>
> Note: Since lately ipv6 has been a hot topic, I'll state that after we get
> the BGP all figured out and working properly, ipv6 is our next project. :)
>
>
>



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