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RE: where to set the default gateway? posted 09/17/2007
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I would run HSRP or VRRP between the 3560s and use those SVIs as your host
gateways.  If you have two VLANs then make one 3560 the active gateway for
one VLAN and the other 3560 the active gateway for the other.  What you are
missing here is an L2 trunk between the two 3560s to make this design solid.


You haven't really said if this actual design is what you are showing or
not.  If this really is all you have then I wouldn't worry too much about
PC2 hitting the first 3560, crossing the L2 trunk to get to the other 3560,
which is the active gateway for that VLAN.  The bandwdith consumption isn't
worth mentioning.  If you would feel better and want a little more bandwidth
and resiliency then make this link an Etherchannel of however many links you
can spare.

If this is just a sample representation and the physical network is really
much larger then the same design principals should still apply.  In this
case you may want to look at some different options, such as Etherchannels
up to the 4506, adding another 4506 for a redundant core, etc.  That seems
to be beyond the scope of your original question however.

You could run L2 to the 4506 as was previously suggested but then you wind
up extending your L2 failure domain and I'm not a real fan of this idea.
One of the main reasons to run L3 from distribution to core (and now now
access on up) is to reduce the L2 failure domain.  There are other reasons
of course, such as much faster L3 convergence but I'm not really looking
there for now.

So here's my suggestion:  Add an L2 trunk between the 3560s and make it an
Etherchannel if you want.  Setup HSRP (or VRRP) between the 3560s and make
them alternate the active gateway for each VLAN (ie sw1 is active for vlan
1, sw2 is active for vlan 2, etc.).  Be sure the STP root matches the active
gateway per VLAN.

Rik

 

-----Original Message-----
From: nobody@xxxxxxxxxxxxxx [mailto:nobody@xxxxxxxxxxxxxx] On Behalf Of
Donghai Zhang
Sent: Monday, September 17, 2007 8:05 AM
To: Alexander Belov
Cc: ccielab@xxxxxxxxxxxxxx
Subject: Re: where to set the default gateway?

the topology may look like this:



                      ---------
                      | 4506 |
                      -----------
                       /     \
                      /         \
                    /            \
            ---------             ----------
            3560 1              35602
            ---------             ----------
             |    |                 |    |
          pc1  pc2             PCs

suppose pc1 in vlan 10 and pc2 in vlan 20,which 3560 acts as the gateway?
if  35602 acts as the getway,should pc1 go through 35601 and then  4506 and
then  35602 and then return along the same route and then back 35601,and
then finally reach pc2?  That seams to be apparently unresonable. But how to
solve it ? You may set gateway just on 35601,but what about PCs under 35602?
Don't they encounter the same situation?


2007/9/17, Alexander Belov <abelov@xxxxxxxxxxxxx>:
>
> Can You draw ? :)
>
> From the bottom story I got You Have 2 (two) distribution layer 
> Switches...
> i.e. 2 x 3560...
> Or You are saying You have two 3560s acting as one switch (like a 
> cluster)?
> :)
>
> WBR,
> Alex
>
> -----Original Message-----
> From: nobody@xxxxxxxxxxxxxx [mailto:nobody@xxxxxxxxxxxxxx] On Behalf 
> Of Donghai Zhang
> Sent: Monday, September 17, 2007 3:01 PM
> To: Marc La Porte
> Cc: ccielab@xxxxxxxxxxxxxx
> Subject: Re: where to set the default gateway?
>
> Maybe I was not telling this clearly. I mean I need one of the 3560s 
> to be the gateway of the PCs in the local LAN. No that there are two 
> 3560s, which one would be proper?
>
> 2007/9/17, Marc La Porte <marc.a.laporte@xxxxxxxxx>:
> >
> > You only have to put a default-gateway on a layer 2 switch, so if 
> > both 3560s are layer 3 then it's not necessary on there
> >
> > On 9/17/07, Donghai Zhang <zdh1207@xxxxxxxxx> wrote:
> > >
> > > Actually the distribute switches will be L3 at this moment. And 
> > > the 3560s would be the default gateways of the hosts.The problem 
> > > is which 3560 to set ?
> > >
> > > 2007/9/17, Marc La Porte <marc.a.laporte@xxxxxxxxx>:
> > > >
> > > > Assuming that the core switch will be L3 and the distribution
> switches
> > > > L2, I would put the SVI on the core switch and the default 
> > > > gateway
> on
> the
> > > > distribution switches
> > > >
> > > > On 9/17/07, Donghai Zhang <zdh1207@xxxxxxxxx > wrote:
> > > > >
> > > > > Dear all,
> > > > > I have got a problem recently. Suppose I have two catalyst 
> > > > > 3560,
> as
> > > > > distribute switch, one catalyst 4506,as core switch. I need to 
> > > > > set default-gateways of those hosts inside local LAN in the
> 3560s.Theploblem is
> > > > > that: in which 3560 should I set the SVI interface? If I set 
> > > > > in
> one,
> > > > > then
> > > > > the hosts within the same vlan but connecting to the other 
> > > > > switch have to travel to this switch so that they can be 
> > > > > servced routing,thus bandwith would be waste.
> > > > > Anyone help me ,thanks advance.
> > > > >
> > > > >
> > > > >
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