hi! We are migrating our eol 29xx edge switch to 45xx and currently all the routing is done in the core sw 65xx. Will it be a good idea to move the routing between vlan to the 45xx switches? (the svr resouces are in different vlan from all the clients' dept vlan) What would be the advantage and disadvantage?
We are also looking at adding another pair of 65xx core sw in our new DC. As the existing 65xx will be configured as the aggreagation/distribution sw with all the dept vlan and hsrp configured on it, what need to be done on the new 65xx to maximize the switching? any new vlan required in the new 65xx to create a L3 link to the old 65xx?
quite new in this kind of setup :) pls advise. Thanks.
L3 from the access-layer is becoming more common but you need to make sure it will fit with your existing vlan setup. For example if you had a buliding with 4 floors and you needed a certain vlan to be spanned across all 4 floors a routed access-layer would not work for you.
That said it does have certain advantages
1) No spanning-tree from the access-layer to the distro/core switches. This is often seen as one of the major pro's although to be fair rapid-pvst+ goes a long way towards alleviating spanning-tree issues. I have used a L3 access-layer where we deployed Nortel VOIP and Nortel don't use STP.
2) Equal cost load-balancing from the access-layer. If each access-layer switch has dual uplinks to the core/distro switches then each access-layer switch sees 2 paths and will use them both. If one fails you will barely notice it, if at all, as all traffic shifts to the one uplink, although you need to make sure that uplink can handle all the traffic. You can achieve this with L2 but it requires manual configuration.
3) Troubleshooting. This is my own opinion but i have found more engineers understand routing a lot better than switching and therefore it is an easier setup to support.
L2 from the access-layer undoubtedly gives more flexibility in terms of vlans and it can be restrictive in a data centre environment but it works well in a campus/building environment.
Your second pair of 6500 switches. Again you can route or you can switch (L2 switch that is). In the good old days, oh dear that makes me sound old :), L2 switching was always recommended because they were far more efficient than routers but now L3 switches can cope perfectly well.
Removing STP from your core is never a bad idea but in a data centre it can be a bit restrictive.
In short there are no right and wrongs and a lot of it comes down to your specific apps/requirements. A very good place to start is with the Cisco design docs -
hi! in your first paragraph, you mentioned that a single vlan can't span multiple L3 edge switch in different floor. Can i achieve that by simply running certain routing procotol, for intervlan routing? Thanks.
What Jon was saying is that in an L3 access layer design, the vlan is confined to the switch that is hosting that vlan. This is called L3 isolation. Remember that a vlan is an L2 broadcast domain and an L3 interface poses a boundary to that. The vlan ends right there.
This may or may not pose a problem for your environment. As Jon points out, in data centers, the L3 access layer perhaps faces its biggest challenge because one usually wants to implement multihoming/NIC teaming -- and for that you need L2 adjacencies.
In my latest engagement, the client had the perfect set up for an L3 access layer, except for the fact that they had a wireless vlan that spanned the entire office. So, we had to go with L2 access.
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