Responding to your good questions:
- Yes, the /14 was a typo. Should be /24.
- Router A is running IOS 11.1
- Router B is running IOS 11.0
- I believe RIP version 1 is used.
- No, he is routing and not bridging. (At least he is attempting to route)
- All other interfaces on either router are on different networks
- With both serial interfaces up/up, router A can ping router B's serial
interface IP
addresses only intermittently and visa-versa. With either serial interface shut
down,
all pings work in all directions.
- I also think this network used to have only one serial link (I believe a T1),
and the
second T1 serial interface was added to increase performance with the intention
of load balancing. I have no idea why both links were put on the same subnet.
Maybe the original person didn't know what he was doing, or he did it this way
to overcome another problem that I am not aware of.
Everything else in both routers' configurations looks pretty innocent except for
the
following:
ip irdp
on Router B's serial 2 interface (This is a completely diifferent serial link
from the
redundant links we've been addressing. I think it has no bearing, but maybe it
does. I
don't know.
If the intent of the redundant serial links is to provide equal-cost
load-balancing,
does putting them on the same subnet open you to unnecessary problems??? What
are your
thoughts??
Thanks,
dj
Kevin Wigle wrote:
> Right off the top I wanted to say "NO! - you can't do this..." but then I
> saw that we were talking about serials here so I did a test. Sure enough I
> was able to put two serial interfaces on the same router into the same
> subnet. Didn't think that was possible. However, as I suspected - as soon
> as I tried to put an Ethernet interface into any subnet in use by any other
> interface - I got the error that it "overlaps" with interface x.
>
> So now we know that Yes you can do it - but will it work.
>
> first - we'll assume that the 192.1.67.202/14 is a typo and it should be
> 192.1.67.202/24
>
> second - let's get rid of the /24 on the transit links
>
> RouterA S0 - 192.1.67.1/30 RouterB S0 - 192.1.67.2/30
> RouterA S1 - 192.1.67.5/30 RouterB S1 - 192.1.67.6/30
>
> third - RIP won't like that so change it to version 2
>
> router RIP
> version 2
>
> (on both routers of course)
>
> or better yet - use EIGRP.
>
> But - you didn't give us any info about where you pinged from, the router?
> a client on the ethernet segment? - what ip address is/are the ethernet
> segments? and what was the destination of the ping??? How is RIP
> configured?
>
> The more I look at it, it seems like a strange network - is he maybe
> bridging and not routing?
>
> That the network is slow isn't too hard to figure. With two interfaces in
> the same subnet the router has to try and figure out - here's a packet - I
> can ship it to:
>
> 1. S0
> 2. S1
> 3. Nowhere - I don't have to!! we're all on the same network!!
> 4. All of the above
> 5. None of the above
> 6. 1 and 2
>
> With only one serial up, the choices become easier.
>
> And are we talking about redundant, x amount of bandwidth required but a
> backup connection?
> Or two circuits load balancing, or a combination?
>
> Too many variables not presented, need more info - perhaps configs??? (and
> design objectives?)
>
> Kevin Wigle
>
> ----- Original Message -----
> From: "Dimitrije" <[EMAIL PROTECTED]>
> To: <[EMAIL PROTECTED]>
> Sent: Sunday, 25 March, 2001 13:13
> Subject: redundant serial links in same subnet??
>
> > I colleague of mine has a network connecting two routers with redundant
> serial
> > links. These serial links happen to reside in the same subnet as follows:
> >
> > Router
> > A
> Router
> > B
> > S0 - 192.1.67.1/24 ----------------------------- 192.1.67.201/24 - S0
> > S1 - 192.1.67.2/24 ----------------------------- 192.1.67.202/14 - S1
> >
> > Both Routers are running RIP.
> >
> > When both links are up, network is very sluggish and ping works
> intermittently
> > (anywhere from 40%-70% of the time) between Routers A & B. When either
> link is
> > shut down (only one link is up at a time), pings work 100% of the time.
> >
> > I'm suspecting that having both serial links in the same subnet is
> creating
> > problems. First of all, can you even do this? Secondly, if you can put
> both
> > serial 0 & 1 in the same subnet, is this creating a layer-2 bridge-loop
> > environment?
> >
> > I think that putting each serial link in a separate sub-net should solve
> the
> > problem, but I don't have access to any equipment to test this.
> >
> > Am I correct or off-base?? Any definitive feedback would be great. Any
> links
> > to spell out the issues with this scenario would also be helpful.
> >
> > thanks,
> > dj
> >
> >
> > _________________________________
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