Re: IPv6 ping on /127 goes one side only

Maxim Denisov · ‎09-08-2020

Hello,

I'm migrating a subnet from a router to 3750x and got a strange IPv6 issue - I can ping switch from the router but can't ping router from switch. At the same time I can ping link local addresses on both sides.

COBALT-RTR#sh ipv6 interface brief g4
GigabitEthernet4       [up/up]
    FE80::250:56FF:FEA0:1274
    2001:470:28:1B5::
COBALT-SW1#sh ipv6 interface brief vlan12
Vlan12                 [up/up]
    FE80::4E00:82FF:FE41:F6C2
    2001:470:28:1B5::1
COBALT-SW1#ping ipv6 FE80::250:56FF:FEA0:1274
Output Interface: vlan12
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to FE80::250:56FF:FEA0:1274, timeout is 2 seconds:
Packet sent with a source address of FE80::4E00:82FF:FE41:F6C2%Vlan12
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/4/17 ms
COBALT-SW1#ping ipv6 2001:470:28:1B5::
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2001:470:28:1B5::, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)

What is the reason? IPv6 unicast routing enabled, sdm prefer set to desktop ipv4 and ipv6 default.

Regards,

Maxim

Georg Pauwen · ‎09-09-2020

Hello,

post the full running configs of both the switch and the router.

Maxim Denisov · ‎09-09-2020

Hello,

Thank you for reply. Here is a config for 3750x:

system mtu routing 1500
!
ip routing
!
ipv6 unicast-routing
!
mls qos
!
spanning-tree mode pvst
spanning-tree extend system-id
!
interface GigabitEthernet1/0/1
 description #-- Cobalt HV1 LAN
 switchport trunk encapsulation dot1q
 switchport mode trunk
!
interface GigabitEthernet1/0/2
 description #-- WAP1
 switchport trunk encapsulation dot1q
 switchport trunk native vlan 10
 switchport mode trunk
!
interface GigabitEthernet1/0/46
 description #-- Cobalt HV1 WAN
 switchport trunk encapsulation dot1q
 switchport trunk native vlan 100
 switchport mode trunk
!
interface GigabitEthernet1/0/47
 description #-- Reserved for second WAN
 switchport access vlan 101
!
interface GigabitEthernet1/0/48
 description #-- Beeline WAN
 switchport access vlan 100
!
interface Vlan1
 description #-- LAN
 ip address 10.255.255.30 255.255.255.224
 ipv6 address 2600:70FF:B018::8:0/64
 ipv6 enable
 ipv6 nd router-preference High
!
interface Vlan11
 description #-- Guest VLAN
 ip address 10.255.255.222 255.255.255.224
!
interface Vlan12
 description #-- RTR-SW
 ip address 100.123.10.14 255.255.255.252
 ipv6 address 2001:470:28:1B5::1/127
 ipv6 enable
!
ipv6 route ::/0 2001:470:28:1B5:: name DEFAULT
!

Ana here is for CSR 1000v:

ipv6 unicast-routing
!
interface Tunnel0
 description #-- Hurricane Electric IPv6 Tunnel Broker
 no ip address
 ipv6 address 2001:470:27:1B5::2/64
 ipv6 enable
 tunnel source 95.31.131.3
 tunnel mode ipv6ip
 tunnel destination 216.66.80.90
!
interface GigabitEthernet4
 description #-- To COBALT-SW1
 ip address 100.123.10.13 255.255.255.252
 ip nat inside
 negotiation auto
 ipv6 address 2001:470:28:1B5::/127
 ipv6 enable
 no mop enabled
 no mop sysid
!
ipv6 route 2600:70FF:B018::/61 2001:470:28:1B5::1 name COBALT-SW1
ipv6 route ::/0 Tunnel0
!

I have stripped blocks that not belong to IPv6 (voice, IPv4 routing protocols, crypto etc.)

cmganoc5561 · ‎09-10-2020

I would try to create a sub-interface in the router with the same IP addresses to receive the tagged packets from VLAN12 interface or you can set the native vlan as VLAN12 in the trunk port to the router. Anyway, the behavior you stated is strange.

Maxim Denisov · ‎09-10-2020

This is not L2 issue because IPv4 works fine and I can ping link local IPv6 addresses on both sides.

Georg Pauwen · ‎09-11-2020

Hello,

which physical port on the switch is connected to the router ? For the sake of testing, put that port in Vlan 12 and make it an access port, e.g.:

nterface GigabitEthernet1/0/1
description #-- Cobalt HV1 LAN
switchport access vlan 12
switchport mode access