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Forum Discussion
Limited number of IPv6 NDP entries
When I configure SDM to use dual-stack (IPv4 and IPv6), I do expect to use both.
However, at least with firmware 11.0.0.31, I get this limits:
(switchcore) #show sdm prefer
The current template is the 'dual ipv4 and ipv6 data center with IP Multicast Support' template.
ARP Entries.................................... 4096
IPv4 Unicast Routes............................ 6112
IPv6 NDP Entries............................... 1024
IPv6 Unicast Routes............................ 3072
ECMP Next Hops................................. 16
IPv4 Multicast Routes.......................... 512
IPv6 Multicast Routes.......................... 256
Maximum VLAN Entries........................... 1024
What is strange is the low limit of IPv6 NDP Entries. For IPv4 hosts, each machine uses one ARP entry. However, for IPv6, you normally use two (link-local and global), but you can use more than that if you are using privacy extension (enable by default on most OS). So, in practice, switch can deal with 4k IPv4 hosts but normally less than 340 IPv6 hosts (1024/3). It can handle about 6k or IPv6 unicast routes, which is far more than hosts. Am I reading this wrongly or something is not well balanced? What will happen when "IPv6 NDP Entries" is exausted?
Switch datasheet says that it has "6K ARP/NDP". I'm guessing it is 6k "shared" between both. However, 4096+1024 is 5K, not 6K. Where did that 1K go? I really need it back.
7 Replies
Hi luizluca,
Welcome to the community!
The maximum ARP/NDP counters is depended on different SDM template.Login the switch by GUI(HTTP/HTTPS), go to 'System'-->'Management'-->'SDM Template Preference', you will see:
1. 'IPv4 Data Center Plus with IP Multicast Support': the 'ARP Entries' is 6144, and the 'IPv6 NDP Entries' is 0;
2. 'IPv4 Data Center Plus without IP Multicast Support': the 'ARP Entries' is 6144, and the 'IPv6 NDP Entries' is 0;
3. 'Dual IPv4 and IPv6 Data Center Plus with IP Multicast Support': the 'ARP Entries' is 4096, and the 'IPv6 NDP Entries' is 1024;
4. 'Dual IPv4 and IPv6 Data Center Plus without IP Multicast Support': the 'ARP Entries' is 4096, and the 'IPv6 NDP Entries' is 1024;
That's mean: if chose dual v4/v6 SDM template, the maximum 'ARP/NDP' counter is 5120; if chose only v4 SDM template, the maximum 'ARP/NDP' counter is 6144;
Hope it helps!
Regards,
EricZ
NETGEAR employeeRetired_Member, thanks for your answer. However, I'm still confuse. You mentinoned "maximum 'ARP/NDP' counter is 5120;" but table shows ARP as "4096" and NPD as "1024". You say that they share a common limit of 5120 (4096+1024)? Aren't they independently managed or NPD can borrow entries from ARP?
No, not share the table size. Just independent for v4 and v6, 4096 ARP table and 1024 NDP table.
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