From: Fred Ingham (fningham@xxxxxxxxxxxxxxxx)
Date: Sat Apr 21 2001 - 00:03:50 GMT-3
Steven: The key to the exercise is in recognizing why S0 of r3 must be
in a blocking state. This is an exercise to emphasize basic bridging
and spanning tree in addition to the stated IRB requirement. ECP1
exercises always have something beyond the obvious.
The overall objective was to ping from the frame switch (r6) interface
to the BVI on r3. If you walk through the basic ping process, you know
that r6 will first send an ARP to the broadcast address to obtain the r3
BVI MAC address. Bridge behavior is to flood a broadcast out all ports
except the port it was received on. So the ARP will go to r2 which is a
two port bridge (e0, and s0). The broadcast will be forwarded out s0 to
r1. R1 is also a two port bridge. The frame multipoint interface is a
single port as is the frame point-to-point interface. Since the
broadcast was received from r2 on the multipoint interface, it will only
be forwarded on the point-to-point interface to r4. But the r4 to r3
path has a blocked port as you have discovered. So, the ARP will never
get to r3. The connectivity is broken.
The solution is to have s0 of r3 in a blocking state thus changing the
r4 to r3 ports on the routers and the catalyst to a forwarding state.
Now the ARP and ping will be forwarded to the BVI. Julia provided a
hint in her post.
The other parts of the exercise were forming the spanning tree with the
specified root and secondary root, and manipulating path cost so the
spanning tree forms to provide the required connectivity. As with all
ECP1 exercises, understanding and identifying the hidden issues is more
important than getting the configuration working.
Cheers, Fred.
Steven Weber wrote:
>
> I am doing this lab and because I am using ethernet and not fastethernet the
> switch port on thr r4 side went into blocking mode. I know that in order to
> get this to work int s0 on r3 must be in blocking but I am not sure as to why
,
> would someone be able to explain this to me please?
> TIA
> Steve
> **Please read:http://www.groupstudy.com/list/posting.html
**Please read:http://www.groupstudy.com/list/posting.html
This archive was generated by hypermail 2.1.4 : Thu Jun 13 2002 - 10:29:53 GMT-3