1. An NP-Based Router for the Open Network Lab Overview by JST
John DeHart

2. JST: Objectives for ONL Router
Reproduce approximately same functionality as current hardware router
routes, filters (including sampling filters), stats, plugins
Extensions
multicast, explicit-congestion marking
Use each NPU as separate 5 port router
each responsible for half the external ports
xScale on each NPU implements CP functions
access to control variables, memory-resident statistics
updating of routes, filters
interaction with plugins through shared memory
simple message buffer interface for request/response

3. JST: Unicast, ARP and Multicast
Each port has Ethernet header with fixed source MAC address – several cases for destination MAC address
Case 1 – unicast packet with destination on attached subnet
requires ARP to map dAdr to MAC address
ARP cache holds mappings – issue ARP request on cache miss
Case 2 – other unicast packets
lookup must provide next-hop IP address
then use ARP to obtain MAC address, as in case 1
Case 3 – Multicast packet
lookup specifies copy-vector and QiD
destination MAC address formed from IP multicast address
Could avoid ARP in some cases
e.g. point-to-point link
but little advantage, since ARP mechanism required anyway
Do we learn MAC Addresses from received pkts?

4. JST: Proposed Approach
Lookup does separate route lookup and filter lookup
at most one match for route, up to two for filter (primary, aux)
combine route lookup with ARP cache lookup
xScale adds routes for multi-access subnets, based on ARP
Route lookup
for unicast, stored keys are (rcv port)+(dAdr prefix)
lookup key is (rcv port)+(dAdr)
result includes Port/Plugin, QiD, next-hop IP or MAC address, valid next-hop bit
for multicast, stored keys are (rcv port)+(dAdr)+(sAdr prefix)
lookup key is (rcv port)+(dAdr)+(sAdr)
result includes 10 bit copy vector, QiD
Filter lookup
stored key is IP 5-tuple + TCP flags – arbitrary bit masks allowed
lookup key is IP 5-tuple + flags if applicable
result includes Port/Plugin or copy vector, QiD, next-hop IP or MAC address, valid next-hop bit, primary-aux bit, priority
Destination MAC address passed through QM
via being written in the buffer descriptor?
Do we have 48 bits to spare?
Yes, we actually have 14 free bytes. Enough for a full (non-vlan) ethernet header.

5. JST: Lookup Processing
On receiving unicast packet, do route & filter lookups
if MAC address returned by route (or higher priority primary filter) is valid, queue the packet and continue
else, pass packet to xScale, marking it as no-MAC
leave it to xScale to generate ARP request, handle reply, insert route and re-inject packet into data path
On receiving multicast packet, do route & filter lookups
take higher priority result from route lookup or primary filter
format MAC multicast address
copy to queues specified by copy vector
if matching auxiliary filter, filter supplies MAC address

6. ONL NP Router (Jon’s Original)
xScale
xScale
add large SRAM ring
TCAM
SRAM Rx
(2 ME)
Mux
(1 ME)
Parse, Lookup, Copy
(3 MEs)
Queue Manager
(1 ME)
HdrFmt
(1 ME) Tx
(2 ME)
Stats
(1 ME)
large SRAM ring
Each output has common set of QiDs
Multicast copies use same QiD for all outputs
QiD ignored for plugin copies
Plugin
Plugin
Plugin
Plugin
Plugin
xScale
SRAM
large SRAM ring