[rbridge] Max Network size / ARP servers

[Guillermo Ibáñez]

Guillermo Ibáñez wrote:

Joe Touch wrote:

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>Guillermo Ibáñez wrote:
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>> would consider big  a network (single broadcast domain) with  25.000
>>-100.000 hosts. But this could fall short.
>>As stated in the paper,  the ARP cache policy in hosts (Windows) is as 
>>follows:  unused entries in last two minutes expire, the refreshed ones 
>>are allowed a maximum of 10 minutes, then a new  ARP request will be 
>>sent. Measurements, (see below at the end of mail) are based on the 
>>current caching at endhosts, so the caching effect  is already included. 
>>Regarding snooping, I agree that snooping of broadcast responses at 
>>proxy-ARPs will reduce the load.
>>    
>>
>
>We agree that this is a problem for a sufficiently large network. As
>I've already noted, there are two things RBridges are not uniquely
>trying to solve:
>	a) increased size of L2 subnets
>	b) insecurity of ARP
>
>Solutions to either should work fine in an RBridge scenario, but are not
>part of the prerequisites of the RBridge architecture.
>
>Although an RBridge may encourage large subnets - larger than are
>currently typical - so do large L2 switches. There are solutions in that
>space to reduce broadcasts (IGMP snooping, proxy ARP, etc.) that might
>apply just fine here, but aren't worth (IMO) mentioning explicitly.
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Agreed, no explicit recommendation of any procedure to reduce broadcasts.

>As you noted, there are plenty of challenges with proxy ARP - hashing,
>load balancing, fault tolerance, etc. But all those solutions will
>benefit all L2 subnet systems, and are not specific to RBridges.
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>>>>Some measurements on ARP load are available at:   
>>>>http://100x100network.org/papers/myers-hotnets2004.pdf
>>>>        
>>>>
Myers extrapolations in the paper are higher ( I do not know his 
rationale) than mine.

>There are also other economies of scale possible in an RBridge -
>broadcasts can be more efficient than in a spanning tree because there
>can be multiple broadcast trees inside the RBridge campus.
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Sorry, I do not catch this argument. Multiple spanning trees are not 
exclusive of Rbridges, any bridge can use them (with MSTP or future 
simplifications or evolutions of it).

>Overall, as said before, I don't think this is an issue specific to
>RBridges. Does anyone else??
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>Joe
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