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Scaling IPv6 Neighbor Discovery

Scaling IPv6 Neighbor Discovery. Ben Mack-Crane ( tmackcrane@huawei.com ). Neighbor Solicitation (RFC4861). Other end-stations are not registered for multicast address. End-station 1 wants to resolve the L2 address of end-station 10;

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Scaling IPv6 Neighbor Discovery

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  1. Scaling IPv6 Neighbor Discovery Ben Mack-Crane (tmackcrane@huawei.com)

  2. Neighbor Solicitation (RFC4861) Other end-stations are not registered for multicast address • End-station 1 wants to resolve the L2 address of end-station 10; • End-station 1 sends Neighbor Solicitation packet using the solicited-node multicast address for end-station 10’s IPv6 address; • The Neighbor Solicitation packet is flooded to all endpoints on the VLAN; • If the end-station 10 has configured its NIC to receive this multicast address, so no other end-stations must process the Neighbor Solicitation packet; • Note: there is a small probability that another end-station could register for the same solicited-node multicast address as end-station 10, but there are 2^24 addresses and so the probability of overlap is small and the impact is small as well (receiving unnecessary solicitations from a few end-stations) and therefore there would be • no significant impact on end-station CPU cycles. 1 2 4 5 6 8 10 3 7 9 End-station 1 sends Neighbor Solicitation End-station 10 receives Neighbor Solicitation

  3. Problems with IPv6 self addressed hosts-What we learned on the way to BOF • When Server is virtualized, • If the server’s MAC filter is smaller than the number of VMs supported, then effectively all the multicast messages will go into the server • impact end station CPU cycles. • For user created subnet, the number of hosts in the subnet is up to the user. • IPv6 gives user more freedom to create a mega size subnet potentially • SLAAC & DAD could potentially blow up DHCP

  4. Unsolicited Neighbor Advertisement All end-stations are registered for all-nodes multicast address • End-station 1 wants to inform all end-stations of a change in L2 address; • End-station 1 sends an Unsolicited Neighbor Advertisement packet using the all-nodes multicast address; • The Unsolicited Neighbor Advertisement packet is flooded to all endpoints on the VLAN; • All end-stations in the VLAN process the Unsolicited Neighbor Advertisement; • Note: this is expected to be a rare event (change of L2 address) and therefore, although all end-stations must process this packet, there would be no significant impact on end-station CPU cycles. 1 2 4 5 6 8 10 3 7 9 End-station 1 sends Unsolicited Neighbor Advertisement Similar to Gratituous ARP Response

  5. ND Scaling Gap Analysis – Performance nodes = routers + hosts; R = #routers; H = #hosts; P = #peers/node; s = small number Scalability looks very good for networks with a few routers and many hosts (each with a few peers) when servers are not virtualized.

  6. ND Scaling Gap Analysis – Performance Additional features and considerations: • Duplicate Address Detection • solicits all-nodes multicast Neighbor Advertisement if address is in use • this should be rare enough to be insignificant • Anycast and Proxy address resolution • solicits multiple Neighbor Advertisements (from each node supporting the Anycast address) • increases the number of Neighbor Advertisements received by the requestor, randomized delay • may want to restrict this feature to a single site in a multi-site network • Neighbor Unreachability Detection • is designed to take advantage of hints from higher layers, only send messages when connectivity is suspect (should be rare) • may not be suitable for core case since each router will have many peers and may not be able to take advantage of higher layer hints – may prefer alternate fault detection methods • Redirect • rate limited, frequency depends on network design and management, impact should be limited • When VMs migration are used, the volume of re-direct could be huge.

  7. ND Scaling Gap Analysis – Performance Additional features and considerations: • Host-based Load Spreading (e.g. RFC 4311) • affects selection of Next Hop Router • does not increase ND traffic appreciably • Router-based Load Spreading (i.e. use of NULL SA in Router Advertisement) • requires hosts to solicit Next Hop Router address • increases solicitations for router addresses • not significant if number of routers is small (may be inappropriate for core) • Holding packet while address resolution occurs • in muiti-site networks or virtualized networks that may increase the edge-to-edge delay, hold time for packets awaiting address resolution may increase significantly • IPv6 Subnet Model (RFC5942) • this RFC does not substantially change ND performance, it simply clarifies that there is no default subnet prefix size and makes small modifications for security

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