Multihomed usecase/dhcpv6: Different ipv6 addresses are getting set/unset on interface when multiple vlans run dhclient and request from same server.
Multihomed usecase/dhcpv6: Different ipv6 addresses are getting set/unset on interface when multiple vlans run dhclient and request from same server.
Isc version: isc-dhcp-4.4.1
Configurations:
SetUP: 40 vlans connected back to back between Client & Server.
Client details: dhclient is running on each vlan. Each of the VLAN(SVI interface) requests for ipv6 IA_NA address and IA_PD prefix from server
Server details: 1 dhcpd server with 40 vlans and conf file having 40 different subnets.
Issue explanation:
When IA_NA & IA_PD are requested from dhclient, we see the from 1st renewal, the ipv6 address/prefix learnt at the client side keep changing. At times even 2 ipv6 address and prefixes were present are present in the VLAN SVI interface.
Sequence of operations between client & server:
- Dhclient: All the vlan interfaces acquire ipv6 addr/prefix from server.(IPV6_ADDRESS_1)
- Dhclient sends renewal upon half lease expiry, in few VLANs dhcpd server replies with NoBinding option.
- Now dhclient starts a new handshake by sending Solicit message. This dhcpd server offers new ipv6 address and prefix (IPV6_ADDRESS_2) ---- > Now interface has 2 ipv6 address and prefix.
- When the lease of V6_ADDRESS_1 expires, it is removed by the dhclient. Now interface has just 1 ipv6 address.
This sequence continues for few VLAN interfaces and affects the underlying networks which was constructed based on the learned prefixes.
Points to be noted:
- ia_na /ia_pd transaction id,device duid are unique for each vlans.
- Dhcpd server lease file is having the details of 1st ipv6 address. Still it returns NoBindings
Please find the attached packet capture of dhclient/dhcp server and dhclient logs.
Thanks & Regards, Revathy Sankarr