| Author |
Source-route bridging question
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| shanelai 2002-05-06, 7:36 am |
| http://www.cisco.com/univercd/illus/c/01/ct842501.gif
When host X sends an explorer frame to host Y, the bridges forward the frame out all ports except the originating port - how does the topology prevent a loop from forming when both bridge 3 and 4 forwards that frame into LAN 2? | |
| shanelai 2002-05-06, 8:02 am |
| To add to this - I thought spanning-tree would prevent the loop by blocking a port on one of the 4 bridges but the Cisco site implies that spanning-tree isn't running.
quote:
In the example in Figure 25-1, this process will yield two routes:
1) LAN 1 to Bridge 1 to LAN 3 to Bridge 3 to LAN 2
2) LAN 1 to Bridge 2 to LAN 4 to Bridge 4 to LAN 2
Host X must select one of these two routes.
If spanning-tree is running, Host X should only receive one route right? | |
| flyfisher 2002-05-06, 3:26 pm |
| I think that seperate explorers goes out each interface then taking note of the bridges and rings that it traverses, when it finds the destination, the direction bit changes and it goes back to the source via the same path it took to get there. The other packet doing the same. The first one to get back to the source is used and the other discarded. Also, correct me if I am wrong but I think spanning tree is not used in SRB.
Thanks. | |
| InfoTechGuy 2002-05-07, 8:30 pm |
| When multiple reply frames reach the source node, it usually uses the route of the first frame recieved. Other decision metrics include the minimum number of hops and the path w/ the largest MTU allowed.
Transparent Bridging - Uses STP to form loop-free paths to the data-link layer destinations. SRB is inherently loop-free and does not rely on STP when delivering data. SRB can use STP when sending explorer frames, thus reducing the traffic generated during route discovery.
Hope this helps
Cheers
-InfoTech |
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