[Xorp-users] Avoiding asynchronous routing with OSPF

[Dirk H. Schulz]

Hi James,

--On 4. September 2008 16:36:42 +0100 James Courtier-Dutton 
<james.dutton at gmail.com> wrote:

> On 12/08/2008, Dirk H. Schulz <dirk.schulz at kinzesberg.de> wrote:
>>
>> The problem I have is that packets from servers in subnet B go out via
>> router2 and answers partially come back via router1. I tried to avoid
>> this by setting interface costs:
>> 1. The hightest interface cost is on eth1 which connects my routers
>> directly (so data traffic between MY routers should be avoided).
>> 2. The interface ethA without virtual ip address A (that is ethA on
>> router2) has a significantly higher cost than the other; with ethB it is
>> similar.
>>
> Do you understand the cost setting in OSPF?
> The ospf cost set on an interface is the cost to SEND packets out.
> The ospf cost set on an interface has no affect on incoming packets.
> I only ask in case you have set the cost on the wrong end of the link.

I did not understand that detail yet, but it does not make any difference 
in my scenario - I have recalculated the path costs with that information.

Seems that my problem is a bit more complicated:
               -------------                  -------------
               |      1     |-----------------|      2     |
upstream routers            |                 |            |
               |            |                 |            |
               -------------                  -------------
                      |                              |
                      |                              |
                      |                              |
               -------------                  -------------
               |      1     |-----------------|      2     |
my routers (connected via eth1)               |            |
               |            |                 |            |
               -------------                  -------------
                  |      |                        |      |
                  |      |                        |      |
                  |      |     -----------        |      |
                   -----------|          |--------       |
switch A (subnet A)           |          |
                         |    |          |               |
                         |     -----------               |
                         |                               |
                         |     -----------               |
                         -----|          |---------------|
switch B (subnet B)           |          |
                              |          |
                               -----------

I want packets destined for subnet B always to come in on my router nr. 2 
(and subnet A vice versa). But if a packet for subnet B arrives on upstream 
router 1, that means it has to do one more hop using upstream router 2 to 
reach my router 2 (compared to going via my router 1).

Can I configure OSPF so that path costs are weighed higher than hop count?

Dirk