Hello,
our network has simplified the following topology: Customers are connected via a switch which is in turn connected to NX-3172PQ. This switch has several vlan interfaces. A DHCP running its service in a different network, so there is a need for a dhcp relay agent. This is configured on this Nexus on all is operated as expected.
Now we want to implement ipv6 as dual stack but the ipv6 relay on the nexus didn’t work as expected because no packets are forwarded towards the dhcpv6 server. The configuration is listed below.
! global
ipv6 dhcp relay
ipv6 dhcp relay source-interface loopback1
interface vlan 100
ipv6 dhcp relay address fe80::70c7:db9c:cd6:a045 inter vlan 101
The output of “show ipv6 dhcp relay” doesn’t show any hints why packets aren't relayed.
device# sh ipv6 dhcp relay
DHCPv6 relay service : Enabled
Relay source interface : loopback1
Insertion of VPN options : Disabled
Insertion of CISCO options : Disabled
DHCPv6 Relay is configured on the following interfaces:
-------------------------------------------------------
Interface Vlan100 :
Relay Address Dest. Interface VRF name
------------- --------------- --------
fe80::70c7:db9c:cd6:a045 Vlan101
device#
Even with several debug command and the use of ethanalyzer I didn’t find out why this feature don’t work. It seems that no traffic is proceeded by this nexus device.
Digging deeper into this issue I found out, that the interface is not listing for multicast traffic to the well know addresse of All_DHCP_Relay_Agents_and_Servers (FF02::1:2). The output of “show ipv6 interface vlan 100” is listed below.
device# sh ipv6 interface vlan 100
IPv6 Interface Status for VRF "default"(1)
Vlan100, Interface status: protocol-up/link-up/admin-up, iod: 11
! output shortend
IPv6 multicast groups locally joined:
ff02::2 ff02::1 ff02::1:ff00:1 ff02::1:ff35:6fc
ff02::1:ff00:0
IPv6 multicast (S,G) entries joined: none
IPv6 MTU: 1500 (using link MTU)
! output shortend
device#
If I configure a device running ios or ios xe with a dhcpv6 relay agent I can observe, that this interface is listing to the multicast address FF02::1:2.
device-ios-xe#sh ipv6 interface lo1
Loopback1 is up, line protocol is up
!output shortend
Joined group address(es):
FF02::1
FF02::2
FF02::5
FF02::1:2
FF02::1:FF00:1
FF02::1:FF26:8100
MTU is 1514 bytes
!output shortend
device-ios-xe#
I was wondering why the dhcp_snoop service is listed as an ipv6 client
device# sh ipv6 client dhcp_snoop
IPv6 Registered Client Status
Client: dhcp_snoop, status: up, pid: 7608, extended pid: 7608
Protocol: (none), pib-index: 10, uuid: 442
Routing VRF id: 65535, flags: 3
Control mts SAP: 360
Data mts SAP: 360
IPC messages to control mq: 16 (failed: 0)
IPC messages to data mq: 0 (failed: 0)
device#
even if the interface is not listing to the multicast address, so I configure another relay agent in the same network as the clients to relay dhcpv6 packets to the unicast address of the nexus device. Now, the nexus device work as a relay agent and encapsulate the reply forward packet into his own reply forward packet and delivered this package to this dhcpv6 server.
My question is, if this behavior is expected. Is a nx os device only capable of relaying unicast dhcpv6 packets or have I miss any configuration to make this scenario work with multicast as well?
Accepted Solutions
