04-17-2008 01:32 AM - edited 03-05-2019 10:26 PM
My question is:
Why am I seeing the IP address of 10.98.3.3 while issue âsh cdp neighbor detailâ on 6513-01? and
why it is using IP address of vlan3 since I have number of the other vlan with IP address configured?
What could be the possible configuration that cause the output as shown by the âsh cdp neighbor detailâ below?
Hope that I am providing enough information, below are the setup.
- 2x 6513 switch trunk together through g1/1 and g2/1.
- It is running in the OSPF environment.
- Both switches are configure with loopback 0 with IP address as 172.16.1.1 and 172.16.1.2 respectively.
- IP address are not configure on both the g1/1 and g2/1 at both the 6513 switch.
- Both the 6513 switches are configure with number of vlans
- the interface g1/1, g2/1 and port-channel 2 are not configure with IP address.
- Noted that the IP address 10.98.3.3 are confiure in 6513-02 it belong to the IP address of interface vlan3.
The 6513 configuration are as follow:
-------------------------------------------------------------------
Both configuration for GigabitEthernet1/1 and GigabitEthernet2/1 are similar:
interface Port-channel2
switchport trunk encapsulation dot1q ; switchport mode trunk; no ip address
interface GigabitEthernet1/1 (and also GigabitEthernet2/1)
switchport; switchport trunk encapsulation dot1q; switchport mode trunk; no ip address
channel-group 2 mode desirable
------------------------------------------------------------
sh cdp neighbor detail
Device ID: DS6513-02.abc.com
Entry address(es):
IP address: 10.98.3.3
Platform: cisco WS-C6513, Capabilities: Router Switch IGMP
Interface: GigabitEthernet2/1, Port ID (outgoing port): GigabitEthernet2/1
-------------------------
Device ID: DS6513-02.abc.com
Entry address(es):
IP address: 10.98.3.3
Platform: cisco WS-C6513, Capabilities: Router Switch IGMP
Interface: GigabitEthernet1/1, Port ID (outgoing port): GigabitEthernet1/1
----------------------------------------------------------------------
interface Vlan3;
ip address 10.98.3.3 255.255.255.0
standby ip 10.98.3.1; standby preempt
router ospf 1
log-adjacency-changes; area 9 stub; summary-address 10.98.0.0 255.255.224.0
passive-interface Vlan3; passive-interface Vlan5
passive-interface Loopback0
network 10.98.0.0 0.0.31.255 area 9
network 10.98.255.0 0.0.0.7 area 9
network 10.98.255.128 0.0.0.7 area 9
thanks in advance
Solved! Go to Solution.
04-17-2008 06:19 AM
CDP will use the lowest number Vlan's Layer3 information to populate the "IP Address" field on the "show cdp neighbor detail" output.
In your case, Vlan3 is the first 'numbered Vlan on switch "DS6513-02.abc.com".
HTH,
__
Edison.
04-18-2008 12:57 AM
Once an adjacency is formed then yes packets can be routed between the 2 switches over the port-channel.
" Assuming that Vlan 4 and vlan 5 are not configure as passive interface, it is true that âsh ip route ospfâ will have the follow output?"
Yes.
Jon
04-17-2008 03:41 AM
hi,
If i am not wrong this is what I understand from your configuration:-
6513--g1/1---trunk----g2/1--6513
is this correct ?
Please do let me know.
Cheers,
Nikhil E.
04-17-2008 07:42 AM
Hi,
My 6513 setup is:
6513 --g1/1 --trunk --g1/1 6513
........ --g2/1 -- "" --g2/1
thank, hope you can help.
04-17-2008 06:19 AM
CDP will use the lowest number Vlan's Layer3 information to populate the "IP Address" field on the "show cdp neighbor detail" output.
In your case, Vlan3 is the first 'numbered Vlan on switch "DS6513-02.abc.com".
HTH,
__
Edison.
04-17-2008 08:05 AM
Hi ediortiz,
I am unable to get the infor, could you kindly provide the link for that info.
thanks
04-17-2008 10:16 AM
It's not documented, I found such behavior by actually trying in a switch.
__
Edison.
04-18-2008 12:12 AM
Edison,
Thanks for your sharing, so, in layer 2 the sh cdp command will show the lower vlan's IP address. This lead to another issue on layer 3, ospf.
At the same 6513-1 and 6513-2
no IP address are configure for both the g1/1 and g2/1 that ârunning port-channel 2â
Under the config:ârouter ospfâ all the vlan are configure as passive interfaces except vlan 4
with the follow output
DS6513-01#sh ip route ospf
O 10.98.255.132/30 [110/2] via 10.98.255.129, 7w0d, GigabitEthernet2/2
[110/2] via 10.98.4.3, 7w0d, Vlan4
O 10.98.1.2/32 [110/2] via 10.98.4.3, 7w0d, Vlan4
My question is why the packet is route through Vlan4? which from my document Vlan4 is the âport-channel 2â which there is no IP address configure on it.
Will it be the same theory like cdp it take the lower vlan? And for this case layer 3 ospf take the lower vlan which in this case not configure as passive interfaces?
Thank in advance.
04-18-2008 12:18 AM
The adjacency is formed because vlan 4 is not passive under your OSPF configuration. Are you saying that vlan 4 has no ip address on either switch ? ie. if you do
sh run int vlan 4
is there an IP address there.
OSPF does not function in the same way as CDP ie. it uses all vlans that are not passive so if none of the vlans were made passive under the router ospf config then you would see an entry in the routing table using each vlan interface.
Does this make sense ?
Jon
04-18-2008 12:54 AM
Sorry, what i mean is that port-channel 2 has no IP address not vlan 4.
- Do you mean the routing is form because of adjacency is form?
- Assuming that Vlan 4 and vlan 5 are not configure as passive interface, it is true that âsh ip route ospfâ will have the follow output?
DS6513-01#sh ip route ospf
O 10.98.255.132/30 [110/2] via 10.98.255.129, 7w0d, GigabitEthernet2/2
[110/2] via 10.98.4.3, 7w0d, Vlan4
[110/2] via 10.98.4.3, 7w0d, Vlan5
thanks
04-18-2008 12:57 AM
Once an adjacency is formed then yes packets can be routed between the 2 switches over the port-channel.
" Assuming that Vlan 4 and vlan 5 are not configure as passive interface, it is true that âsh ip route ospfâ will have the follow output?"
Yes.
Jon
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