IPv6 Neighbors

[gongya001]

R1-Router
interface Ethernet0/0
 no ip address
 ipv6 address 2001:10::1/64
 ipv6 enable
 ipv6 nd other-config-flag
 ipv6 nd ra dns server 4::4
 ipv6 dhcp server DHCP-POOL
R2-host
interface Ethernet0/0
 no ip address
 ipv6 address autoconfig
 ipv6 enable
R2-Host#show ipv6 int bri e0/0
Ethernet0/0            [up/up]
    FE80::A8BB:CCFF:FE00:200
    2001:10::A8BB:CCFF:FE00:200
R3-Attacker
interface Ethernet0/0
 no ip address
 ipv6 address autoconfig
 ipv6 enable
R3-Attacker#show ipv6 int bri e0/0
Ethernet0/0            [up/up]
    FE80::A8BB:CCFF:FE00:C00
    2001:10::A8BB:CCFF:FE00:C00
end
I got the following neighbors

R1-Router#show ipv6 nei
IPv6 Address                              Age Link-layer Addr State Interface
FE80::A8BB:CCFF:FE00:200                    0 aabb.cc00.0200  REACH Et0/0
FE80::A8BB:CCFF:FE00:C00                    0 aabb.cc00.0c00  REACH Et0/0

R2-Host#show ipv6 nei
IPv6 Address                              Age Link-layer Addr State Interface
FE80::A8BB:CCFF:FE00:600                    0 aabb.cc00.0600  REACH Et0/0
R3-Attacker#show ipv6 nei
IPv6 Address                              Age Link-layer Addr State Interface
FE80::A8BB:CCFF:FE00:200                   47 aabb.cc00.0200  STALE Et0/0
FE80::A8BB:CCFF:FE00:600                    0 aabb.cc00.0600  REACH Et0/0

My questions are:
1. why R2 is not neighboring with R3 ?
2. Why the neighbor state keeps changing from among delay, stale and reach ?
thanks !!

[johnd2310]

Hi,

1. Probably R2 has not talked to R3 yet. Try to ping R3 from R2  and check state
2.  you can get meaning at the following link: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipv6/command/ipv6-cr-book/ipv6-s4.html

Table 9 show ipv6 neighbors Field Descriptions

Field	Description
IPv6 Address	IPv6 address of neighbor or interface.
Age	Time (in minutes) since the address was confirmed to be reachable. A hyphen (-) indicates a static entry.
Link-layer Addr	MAC address. If the address is unknown, a hyphen (-) is displayed.
State	The state of the neighbor cache entry. Following are the states for dynamic entries in the IPv6 neighbor discovery cache: INCMP (Incomplete)--Address resolution is being performed on the entry. A neighbor solicitation message has been sent to the solicited-node multicast address of the target, but the corresponding neighbor advertisement message has not yet been received. REACH (Reachable)--Positive confirmation was received within the last ReachableTime milliseconds that the forward path to the neighbor was functioning properly. While in REACH state, the device takes no special action as packets are sent. STALE--More than ReachableTime milliseconds have elapsed since the last positive confirmation was received that the forward path was functioning properly. While in STALE state, the device takes no action until a packet is sent. DELAY--More than ReachableTime milliseconds have elapsed since the last positive confirmation was received that the forward path was functioning properly. A packet was sent within the last DELAY_FIRST_PROBE_TIME seconds. If no reachability confirmation is received within DELAY_FIRST_PROBE_TIME seconds of entering the DELAY state, send a neighbor solicitation message and change the state to PROBE. PROBE--A reachability confirmation is actively sought by resending neighbor solicitation messages every RetransTimer milliseconds until a reachability confirmation is received. ????--Unknown state. Following are the possible states for static entries in the IPv6 neighbor discovery cache: INCMP (Incomplete)--The interface for this entry is down. REACH (Reachable)--The interface for this entry is up. Note    Reachability detection is not applied to static entries in the IPv6 neighbor discovery cache; therefore, the descriptions for the INCMP (Incomplete) and REACH (Reachable) states are different for dynamic and static cache entries.
Interface	Interface from which the address was reachable.

Thanks

John

[gongya001 · Accepted solution]

R2-Host#show ipv6 int bri e0/0
Ethernet0/0            [up/up]
    FE80::A8BB:CCFF:FE00:200
    2001:10::A8BB:CCFF:FE00:200

R3-Attacker#show ipv6 int bri e0/0
Ethernet0/0            [up/up]
    FE80::A8BB:CCFF:FE00:C00
    2001:10::A8BB:CCFF:FE00:C00

R2-Host#ping ipv6 FE80::A8BB:CCFF:FE00:C00
Output Interface: ethernet0/0
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to FE80::A8BB:CCFF:FE00:C00, timeout is 2 seconds:
Packet sent with a source address of FE80::A8BB:CCFF:FE00:200%Ethernet0/0
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/5/21 ms

R3-Attacker#ping ipv6  FE80::A8BB:CCFF:FE00:200
Output Interface: ethernet0/0
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to FE80::A8BB:CCFF:FE00:200, timeout is 2 seconds:
Packet sent with a source address of FE80::A8BB:CCFF:FE00:C00%Ethernet0/0
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/1 ms

I noticed the neighbor is established after R2 and R3 ping each other.

thanks !!