peering exchange architectures jeff bartig university of wisconsin wiscnet engineering
TRANSCRIPT
Overview OmniPOP - new CIC R&E exchange in
Chicago Way too many hours of conference calls
about hardware and architecture of OmniPOP
I returned Paul Schopis’ phone call.
Layer 2 Shared Exchange Layer 2 switch Each peer connects to
switch Single broadcast
domain Generally a single
subnet allocated - each peer gets an address out of the block
Used at many commercial exchanges
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Layer 2 shared - Pros/ConsCons
Single broadcast domain
Peer abuse possible Broadcast traffic Multicast difficulties Per-peer statistics more
difficult to collect (per-MAC address stats necessary)
Single MTU size
Pros Easy/Simple No exchange provider
involvement needed to establish a new peer
Many peers on a single port - lower cost
Layer 2 VLAN Exchange Each peer has a
trunk interface on layer 2 exchange switch
Each peer may have a VLAN to every other peer
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Layer 2 VLAN Exchange Each peer has a
trunk interface on layer 2 exchange switch
Each peer may have a VLAN to every other peer
(n * (n-1)/2 VLANs for a full mesh
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Layer 2 VLAN - Pros/ConsPros
Separation MTU per VLAN Multicast easier Many peers on a single
port - lower cost Logical interface stats
Cons Many VLANs VLAN conflicts
possible Exchange provider
involvement if VLANs are not preallocated
Layer 1 No central exchange
hardware Each peer
establishes cross connects to parties they want to peer with
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Layer 1 Pros/Cons Requires an
interface for each peer
No exchange provider hardware needed - may be a cost savings
Capacity/protocol flexibility
Layer 3 Exchange Each peer gets a
port on the exchange router
Each peer establishes a BGP session with exchange router
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Layer 3 - Pros/ConsCons
Less control Routing policy
determined by exchange provider
Extra AS hop in path, possible impact on routing decisions
Pros Simpler Single BGP session No need for a
peering coordinator - outsourcing to exchange provider
Layer 3 Exchange - AS-path Length Concern Example
Peer to WN AS PathsLayer 2 Exchange
2381 701 2381 WN direct peer shorter
Layer 3 Exchange 54321 2381 701 2381 Equal paths. Which one will be
chosen by peer?
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AS-Path Length Experiment WiscNet peers with 31 networks at Equinix-
Chicago What difference would it make if we instead
did this peering via a layer 3 exchange? Depends upon the routing policies of the peers (local pref wins over AS-path length)
Prepended extra AS hops into the advertisements to see what would happen.
AS-Path Length Experiment Results
13:50 - prepended extra hop
450 to 350Mb/s drop 22% loss
14:26 - prepended 2nd extra hop
410 to 350Mb/s drop additional 15% loss
14:45 - removed all prepending
310 to 430Mb/s increase 38% increase