Dell PowerSwitch S4820T Configuration Guide for the S4820T System 9.112.0P1 - Page 237
Catch-All Entry for IPv6 Packets, xSTP, FRRP, LACP, 802.1x, ECFM, L2PT, TRILL, Open
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Page 237 highlights
• NDP Packets in VLT peer routing enable • VLT peer routing enable cases each VLT node will have route entry for link local address of both self and peer VLT node. Peer VLT link local entry will have egress port as ICL link. And Actual link local address will have entry to CopyToCpu. But NDP packets destined to peer VLT node needs to be taken to CPU and tunneled to the peer VLT node.. • NDP packets in VLT peer routing disable case • NDP packets intended to peer VLT chassis taken to CPU and tunnel to peer. The following table describes the protocol to queue mapping with the CPU queues increased to be 12. Table 12. Redirecting Control Traffic to 12 CPU queues CPU Queue Weights Rate (pps) 0 100 1300 1 1 300 2 2 300 3 4 4 127 5 16 6 16 7 64 8 32 9 64 10 32 11 32 400 2000 300 400 400 400 600 300 300 Protocol BFD MC TTL0, TTL1, IP with options, Mac limit violation, Hyper pull, L3 with Bcast MacDA, Unknown L3, ARP unresolved, ACL Logging sFlow, L3 MTU Fail frames IPC/IRC, VLT Control frames ARP Request, NS, RS, iSCSI OPT Snooping ICMP, ARP Reply, NTP, Local terminated L3, NA, RA,ICMPv6 (other Than NDP and MLD) xSTP, FRRP, LACP, 802.1x,ECFM,L2PT,TRILL, Open flow PVST, LLDP, GVRP, FCOE, FEFD, Trace flow OSPF, ISIS, RIPv2, BGP DHCP, VRRP PIM, IGMP, MSDP, MLD Catch-All Entry for IPv6 Packets Dell Networking OS currently supports configuration of IPv6 subnets greater than /64 mask length, but the agent writes it to the default LPM table where the key length is 64 bits. The device supports table to store up to 256 subnets of maximum of /128 mask lengths. This can be enabled and agent can be modified to update the /128 table for mask lengths greater than /64. This will restrict the subnet sizes to required optimal level which would avoid these NDP attacks. The IPv6 stack already supports handling of >/64 subnets and doesn't require any additional work. The default catch-all entry is put in the LPM table for IPv4 and IPv6. If this is included for IPv6, you can disable this capability by using the no ipv6 unknown-unicast command. Typically, the catch-all entry in LPM table is used for soft forwarding and generating ICMP unreachable messages to the source. If this is in place then irrespective of whether it is /64 subnet, it doesn't have any effect as there would always be LPM hit and traffic are sent to CPU. Unknown unicast L3 packets are terminated to the CPU CoS queue which is also shared for other types of control-plane packets like ARP Request, Multicast traffic, L3 packets with Broadcast MAC address. The catch-all route poses a risk of overloading the CPU with unknown Control Plane Policing (CoPP) 237
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