DLSw question

Question

Dear all,
Could anyone help me to clarify the following point on DLSw redundancy?
Is it true if DLSw redundancy (or recover) are transparent to user if the end stations lie on a token ring network ? On the other hand if the end stations lie on the ethernet LAN, the DLSw can re-established itself but it is not transparent to user. Can I make such a conclusion ?
thanks

Answer 1

Hi,
no, this statement is not true.
From an end systems perspective the recovery is always disruptive. No matter if you are on a tokenring or on a ethernet lan.
That means:
DLSw is about llc2 sessions at layer2. If your lan attached end system has a llc2 session with a cisco dlsw router and i.e. that router fails, the llc2 session with the end system will fail aswell.
After the end system has realized that the llc2 session is gone it cleans up its local connections and then tries to reestablish the llc2 connection. If another dlsw router is available, who can reach the requested remote host, than this connection will come up again. That means the end user sna session goes down and comes back up again.
The same is true if you are talking about dlsw+ ethernet redundancy.
There is more in the details/differences between ethernet and tokenring lan segments. I.e. on a tokenring you have a rif in each packet which can be used for loop control.
On ethernet you almost always have ethernet switches, where a cam table of a ethernet switch in any vlan for any mac address can only point to exactly one port on the switch.
If you have two dlsw routers connected that can reach the same remote host those two routers will both send frames with the same host mac address into the same switch on two different ports. This is where dlsw ethernet redundancy feature comes into play.
thanks...
Matthias