How many switches can be daisy-chained ?

mflak · ‎12-22-2002

Can I daisy-chain 12 Catalyst switches using 1 Gb/s links ? What I want to achive is chain that span more than 180 km between switches placed on the edge (The diameter of the broadcat domain (vlan) will be 180 km). Average distans between nodes is 15-20 km and I plan to use GBIC-ZX. I paln to use Cat 3550-12G and inter-vlan routing but for some VLAN I can't use routing and they should span over all 12 switches. It is possible ? It is good solution ? about STP limitations ?

What

Thanks for any suggestions !!!

efrahim · ‎12-22-2002

Hi,

12 switches in the daisy chain, is usually not considered as good design. Although there is no limitaion but 7 switches is what is recommnended.

http://www.cisco.com/warp/customer/473/16.html

mflak · ‎12-23-2002

Thanks for information, could you give me explanation if this limitation to 7 node is due to STP or is depending on something else. If I switch STP off could I use more then 7 switches in daisy-chain. Performance and troubleshooting issue is not problem form me for this design.

Thanks !!!

vincent-n · ‎01-05-2003

Hi there

I don't agree with one of the comment that you can daisy-chained 12 switches together as due to STP. STP in theory can span a whole load more than 12 switches and there is no documented limit on how many "hops" you can have between your root and edge switches. The number 7 recommended by Cisco (I think) is due to latency and the fact that if your workstation at one end has to wait longer than it supposed to wait for a packet, it will consider that packet is lost. If you daisy-chained your switches to more than 7 switches, Cisco (and other vendors) cannot gurantee that the packet will get to where it supposed to and back in time so that your workstation does not assume that the packet is lost during transmission.

I would recommend that in your network topology, have a router setup at each site and have them connected together on one single VLAN. This VLAN is considered to be a WAN VLAN. At each site, you can have whatever VLAN you'd like and route to each office via the WAN VLAN. I have setup a network like this before and it runs beautifully (the WAN VLAN was an FDDI ring).

Prashanth Krishnappa · ‎12-23-2002

You can have 12 switches daisy chained. The 7 switches recommendation is from the STP root switch. Make sure the STP root switch is somewhere in the middle so that you do not have more than 7 switches on either side