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Beginner

Re: EIGRP Neighbor flapping between Core's on VLAN 48

ARP provides the IP address to MAC address mapping so a unicast packet will be delivered to the correct device.  For example in my testbed I have the following:

1#sh ip ei nei

EIGRP-IPv4 Neighbors for AS(100)

H   Address                 Interface       Hold Uptime   SRTT   RTO  Q  Seq

                                            (sec)         (ms)       Cnt Num

0   10.1.12.2               Et0/0             11 00:00:13   36   216  0  3

r1#sh ip arp 10.1.12.2

Protocol  Address          Age (min)  Hardware Addr   Type   Interface

Internet  10.1.12.2               0   aabb.cc00.0200  ARPA   Ethernet0/0

r1#

r2#sh int e0/0 | i address

  Hardware is AmdP2, address is aabb.cc00.0200 (bia aabb.cc00.0200)

  Internet address is 10.1.12.2/24

r2#

So the MAC address of r2 matches the ARP entry r1 has for that peer. If you have a duplicated IP address, it's possible that the ARP entry is populated with the MAC address of the "other" owner of the IP address and will mess up EIGRP's ability to work.

Highlighted
Beginner

Re: EIGRP Neighbor flapping between Core's on VLAN 48

I also see the difference you are using is ether port instead of vlan on your sh ip ei nei

I can see you are doing the arp to ip and then mac address to port.  I have traced that down as well on interface,

here is the output from the 3750e

#show arp | i 10.200.0.13

Internet  10.200.0.13             -   68ef.bdf4.dcc3  ARPA   Vlan48

3750e#show mac add

3750e#show mac address-table | i 68ef.bdf4.dcc3

3750e#show arp | i 10.200.0.14

Internet  10.200.0.14           134   0012.da27.9f00  ARPA   Vlan48

3750e#show mac address-table | i 0012.da27.9f00

  48    0012.da27.9f00    DYNAMIC     Po48

  90    0012.da27.9f00    DYNAMIC     Po47

here is the output from the 6513

6513 flapping#show arp | i 10.200.0.14

Internet  10.200.0.14             -   0012.da27.9f00  ARPA   Vlan48

6513 flapping#show mac add

6513 flapping#show mac address-table | i 0012.da27.9f00

*  399  0012.da27.9f00    static  No           -   Router

*  398  0012.da27.9f00    static  No           -   Router

*  391  0012.da27.9f00    static  No           -   Router

*   50  0012.da27.9f00    static  No           -   Router

*   48  0012.da27.9f00    static  No           -   Router

*   46  0012.da27.9f00    static  No           -   Router

*   23  0012.da27.9f00    static  No           -   Router

*    4  0012.da27.9f00    static  No           -   Router

*   93  0012.da27.9f00    static  No           -   Router

*   90  0012.da27.9f00    static  No           -   Router

*  501  0012.da27.9f00    static  No           -   Router

*  500  0012.da27.9f00    static  No           -   Router

*  ---  0012.da27.9f00    static  No           -   Router

*  608  0012.da27.9f00    static  No           -   Router

*  607  0012.da27.9f00    static  No           -   Router

*  606  0012.da27.9f00    static  No           -   Router

*  605  0012.da27.9f00    static  No           -   Router

*  604  0012.da27.9f00    static  No           -   Router

*  603  0012.da27.9f00    static  No           -   Router

*  602  0012.da27.9f00    static  No           -   Router

*  601  0012.da27.9f00    static  No           -   Router

*  600  0012.da27.9f00    static  No           -   Router

*  361  0012.da27.9f00    static  No           -   Router

*  362  0012.da27.9f00    static  No           -   Router

*  352  0012.da27.9f00    static  No           -   Router

*  353  0012.da27.9f00    static  No           -   Router

*  351  0012.da27.9f00    static  No           -   Router

*  343  0012.da27.9f00    static  No           -   Router

*  342  0012.da27.9f00    static  No           -   Router

*  341  0012.da27.9f00    static  No           -   Router

*  331  0012.da27.9f00    static  No           -   Router

*  334  0012.da27.9f00    static  No           -   Router

*  335  0012.da27.9f00    static  No           -   Router

*  332  0012.da27.9f00    static  No           -   Router

*  333  0012.da27.9f00    static  No           -   Router

*  322  0012.da27.9f00    static  No           -   Router

*  321  0012.da27.9f00    static  No           -   Router

*  151  0012.da27.9f00    static  No           -   Router

*  311  0012.da27.9f00    static  No           -   Router

*  314  0012.da27.9f00    static  No           -   Router

*  315  0012.da27.9f00    static  No           -   Router

*  312  0012.da27.9f00    static  No           -   Router

*  313  0012.da27.9f00    static  No           -   Router

6513 flapping#show arp | i 10.200.0.13

Internet  10.200.0.13           137   68ef.bdf4.dcc3  ARPA   Vlan48

6513 flapping#show mac address-table | i 68ef.bdf4.dcc3

*   48  68ef.bdf4.dcc3   dynamic  Yes          0   Po3

what can you tell from this donald

Highlighted
Beginner

Re: EIGRP Neighbor flapping between Core's on VLAN 48

That was useful, mainly to make me go back and look at your earlier output.  :^)

I stated that you had multicast both ways but unicast broken and I was wrong.  You're missing all traffic one direction (assuming what you did immediately above makes sense.)  I'll paste it back in here:

From the 6513:

show ip eigrp neighbors

IP-EIGRP neighbors for process 500

H   Address                 Interface       Hold Uptime   SRTT   RTO  Q  Seq

                                            (sec)         (ms)       Cnt Num

0   10.200.0.13             Vl48              10 00:00:42    1  5000  2  0

From the 3750e:

show ip eigrp neighbors

EIGRP-IPv4 Neighbors for AS(500)

H   Address                 Interface       Hold Uptime   SRTT   RTO  Q  Seq

                                            (sec)         (ms)       Cnt Num

0   10.200.0.10             Vl47              13 8w5d        3   200  0  4226

In the output directly above you are displaying the addresses 10.200.0.13 and 10.200.0.14 on VLAN48.  Notice that the 3750 doesn't even have a peer on VLAN 48 and certainly doesn't see 10.200.0.14.  I was hasty in my judgement that it was a unicast problem. Instead, you don't have any of EIGRP traffic received on the 3570 from the 6500 in VLAN48.

BTW, I also wanted to clarify what I said earlier for your education.  What I did was look up the IP address of the peer and then find the ARP that matches that peer to get the MAC address. I then went to the peer to look at the MAC address associated with the interface used to reach the first peer I checked the ARP on to make sure they matched. 

It looks to me like you looked up the ARP entry for the local interface instead.  In other words, the 6500's interface address was 10.200.0.14 and you looked up the ARP entry for that address on the 6500, and looked up 10.200.0.13 on the 3750.  This is backwards.

Highlighted
Beginner

Re: EIGRP Neighbor flapping between Core's on VLAN 48

Well, I see that 3750e does not show the vlan 48 in the eigrp neigbors listed.  That cant be good and maybe a reason why i am getting flapping as well.

Since i am not posting the correct information can you please post the correct commands please?

Thank you for your help and sorry for the very late reply.

Highlighted
Beginner

Re: EIGRP Neighbor flapping between Core's on VLAN 48

Check BPDUGUARD

Sent from Cisco Technical Support iPhone App

Highlighted
Beginner

Re: EIGRP Neighbor flapping between Core's on VLAN 48

Ok I will check this as well

I will post what i find on this issue and thank you to very for helping with this problem

Beginner

Re: EIGRP Neighbor flapping between Core's on VLAN 48

Hi Adam,

Please check the MTU of the Vlan 48 and physical port that connect the two swtches.

#show int vlan48 | i MTU

#show int GigabitEthernet x/y | i MTU

If the MTU diffrence is highly mismatched between the two switches it can cause the neighborship flapping.

Set it to equal or close values. See if that solves the problem

Highlighted
Beginner

Re: EIGRP Neighbor flapping between Core's on VLAN 48

OK, last night I work with the ideas I got from here and also work with Cisco TAC.

EIGRP: Packet from ourselves ignored    this problem was fixed by change the loopback0 from non-passive interface to passive interface.

The EIGRP flapping was still happening

So from the debugs that the cisco tac did we saw that 6513 was sending and recieving hellos packets, but the 3750e was not receiving the hello packets but was sending them. 

So what seem to fixed this problem was on the 6513 we turn off vtp purning and clear ip eigrp neighb command

After that 3750e and 6513 flapping stop

So this problem has been fixed sorry i did not save the debugging I close the wrong ssh session and lost it. 

Highlighted
Beginner

Re: EIGRP Neighbor flapping between Core's on VLAN 48

How, do I close this question since I got the answer and fixed this problem?

Anyone