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show ip mroute count interpertation

I've inherited a configuration, and I'm trying to understand it. 

Almost all of our L3 switches have a command:
ip multicast route-limit 500

But I'm not sure how the switch (3750) is interpreting this.

Running a:
sho ip mroute count

results with the following information:

Multicast route-limit: 500
IP Multicast Statistics
434 routes using 1738880 bytes of memory
44 groups, 8.86 average sources per group

Then all of my groups, with all of the sources for each group.

So each Source, in every group, is counted as a route?

The reason I ask, we're upping the number of devices we're using (So more sources will show up, each device joins three multicast groups as a sender)

So that limit should be (in my case since each device joins three groups) Number of devices * 3 plus a fudge factor ?

 

1 ACCEPTED SOLUTION

Accepted Solutions
Hall of Fame Super Blue

I don't have a switch to test

I don't have a switch to test with but i assume it is working it out as follows -

1) each group will have a (*, <group IP address>) in the mroute table so 44 of those.

2) then for each group there are 8.86 average source so  44 * 8.86 = 389.94 so 390.

3) 390 + 44 = 434 which is what exactly what your mroute count is showing.

each source creates a new entry per group in the mroute table. If you pick a couple of groups and look at the mroute table you should see multiple entries for that group address with different source IPs.

It's worth doing the above just in case i am interpreting it incorrectly.

In terms of the limit if the number of groups isn't changing then you just need to account for the increase in source specific entries in the mroute table. If each new source is going to join three groups then yes the number of additional entries should be as you suggest.

Jon

1 REPLY
Hall of Fame Super Blue

I don't have a switch to test

I don't have a switch to test with but i assume it is working it out as follows -

1) each group will have a (*, <group IP address>) in the mroute table so 44 of those.

2) then for each group there are 8.86 average source so  44 * 8.86 = 389.94 so 390.

3) 390 + 44 = 434 which is what exactly what your mroute count is showing.

each source creates a new entry per group in the mroute table. If you pick a couple of groups and look at the mroute table you should see multiple entries for that group address with different source IPs.

It's worth doing the above just in case i am interpreting it incorrectly.

In terms of the limit if the number of groups isn't changing then you just need to account for the increase in source specific entries in the mroute table. If each new source is going to join three groups then yes the number of additional entries should be as you suggest.

Jon

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