04-09-2014 03:41 AM - edited 03-04-2019 10:45 PM
Hi,
I have a problem with connecting my router 2800 to another router 2800.
Both routers only have one interface FastEthernet 0/0 available, the other one os allready taken. This part is simple I put the ips on both interfaces and the connect to each other.
Here comes the problem. The first router is a mobile router, Its not allways connected to the same second router. I have about 15 secoond router (all are the same 2800 series with same ios). So I would like to connect to all my second routers withot reconfiguring the first one each time I go to another one.
example:
Router 1 (the mobile one)
Interface FastEthernet 0/0
ip address 10.0.0.1 255.255.255.252
Router 2
Interface FastEthernet 0/0
ip address 10.0.0.2 255.255.255.252
Router 3
Interface FastEthernet 0/0
ip address 10.0.0.6 255.255.255.252
Router 4
Interface FastEthernet 0/0
ip address 10.0.0.10 255.255.255.252
I tried with entering secondary ip address but I only worked one way, I could ping the the first router but the first could ping the second router and the EIGRP didn`t work.
interface FastEthernet0/0
ip address 10.0.0.1 255.255.255.252
ip address 10.0.0.5 255.255.255.252 secondary
ip address 10.0.0.9 255.255.255.252 secondary
I tried using subinterfaces but I didnt even get a ping through.
interface FastEthernet0/0
no ip address
duplex auto
speed auto
!
interface FastEthernet0/0.1
encapsulation dot1Q 2
ip address 10.0.0.1 255.255.255.252
!
interface FastEthernet0/0.2
encapsulation dot1Q 3
ip address 10.0.0.5 255.255.255.252
Solved! Go to Solution.
04-09-2014 02:05 PM
Hello,
You can achieve this with sub-interfaces. Take for instance the below scenario.
R1 has multiple sub-interfaces - one physical interface that can be attached to one interface of another router at any time, and also form an EIGRP neighborship. This instance I will connect R1 and R2 but using multiple IP's to demonstrate that neighborship is formed on both interfaces.
Here is R1
R1#show ip int brie
Interface IP-Address OK? Method Status Protocol
FastEthernet0/0 unassigned YES TFTP up up
FastEthernet0/0.1 1.1.1.1 YES manual up up
FastEthernet0/0.2 2.2.2.1 YES manual up up
interface FastEthernet0/0
no ip address
duplex auto
speed auto
!
interface FastEthernet0/0.1
encapsulation dot1Q 1 native
ip address 1.1.1.1 255.255.255.0
!
interface FastEthernet0/0.2
encapsulation dot1Q 2
ip address 2.2.2.1 255.255.255.0
router eigrp 100
network 1.1.1.1 0.0.0.0
network 2.2.2.1 0.0.0.0
no auto-summary
I have connected R2 with multiple IP's exactly the same.
R2
interface FastEthernet0/0
no ip address
duplex auto
speed auto
!
interface FastEthernet0/0.1
encapsulation dot1Q 1 native
ip address 1.1.1.2 255.255.255.0
!
interface FastEthernet0/0.2
encapsulation dot1Q 2
ip address 2.2.2.2 255.255.255.0
router eigrp 100
network 1.1.1.2 0.0.0.0
network 2.2.2.2 0.0.0.0
no auto-summary
See the EIGRP adjacencies here:
R1
R1#show ip eigrp neigh
IP-EIGRP neighbors for process 100
H Address Interface Hold Uptime SRTT RTO Q Seq
(sec) (ms) Cnt Num
1 2.2.2.2 Fa0/0.2 11 00:06:30 26 200 0 8
0 1.1.1.2 Fa0/0.1 11 00:07:26 27 200 0 5
R2
R2#show ip eigrp neighbors
IP-EIGRP neighbors for process 100
H Address Interface Hold Uptime SRTT RTO Q Seq
(sec) (ms) Cnt Num
1 2.2.2.1 Fa0/0.2 11 00:07:22 1281 5000 0 7
0 1.1.1.1 Fa0/0.1 14 00:08:18 35 210 0 4
In your case Router 1 (the mobile one) should match the sub-interface encapsulation and tag of the respective routers.
i.e.
R1 (dot1q tag 2 is to R2)
R1 (dot1q tag 3 is to R3)
Making sure its the same on both sides.
Hope this satisfies the requirement and helps.
If you have already tried the above, please check ip addressing is correct and that EIGRP config is also correct. And lastly, if this still doesn't work, try having one connection as native - I don't believe this should make a difference but the IOS might behave this way for odd reasons.
I just tested the above and works fine.
04-09-2014 05:20 AM
You could use DHCP on the mobile router interface and then configure an IP pool on each of your other routers eg. -
mobile router -
int fa0/0
ip address dhcp
router eigrp 10
network 10.0.0.0 0.0.0.255 <-- this needs to cover all the /30s on the other routers so whichever 10.0.0.x IP the mobile router gets this network statement covers it
using router 3 as an example -
ip dhcp pool MOBILE
network 10.0.0.4 255.255.255.252
ip dhcp excluded-address 10.0.0.6
router eigrp 10
network 10.0.0.4 0.0.0.3
then each time the mobile router was reconnected to another router it would pick up the correct 10.x.x.x address for that subnet and then form an EIGRP neighborship.
Jon
04-09-2014 10:49 AM
Sweet suggestion did not think of that.
But unfortunately our company security policy does not allow DHCP addressing I can only use static IP addresses.
Thx for the suggestion
04-09-2014 01:08 PM
I understand about the security policy.
Don't forget though that you could always do a manual binding in the the DHCP pool so only the mobile router could actually get that IP.
I appreciate that still may not be acceptable.
What's not clear is what is connected to each router on their fa0/0 interfaces if they are not connected to the mobile router ?
If it is nothing then why not simply increase the subnet mask for the connection ?
Jon
04-09-2014 11:28 PM
I agree with Jon Marshall,
It is simple to have the mask 255.255.255.224.
BR
Thanveer
"Please rate the helpful posts"
04-09-2014 08:20 AM
The problem is that using those ip address, interfaces of different routers are on different subnets, so thay have no route for the others networks; for example router with address 10.0.0.10 255.255.255.252 doesn't konw how to route to network 10.0.0.1 255.255.255.252
When using secondary ip you have to ping specifing the secondary ip source on R1, otherwise it use primary ip: ping 10.0.0.6 sou 10.0.0.5
EIGRP does not make neighborship on seconadry ip address, it can advertise seconadry network but neighborship is built only on primary ip address
Subinterf doesn't help you: you have exactly the same ip addressing and problems) but using 802.1q encasulation between routers
Bye,
e
04-09-2014 10:55 AM
Yes I realize that using secondary ip addresses or subinterfaces does not work. I am looking for someone that can help me solve my problem or steer me in the right direction, like Jon Marshall that suggested that I try with DHCP (thx again for that Jon).
But thank you for explaining why my solutions don`t work.
04-09-2014 02:05 PM
Hello,
You can achieve this with sub-interfaces. Take for instance the below scenario.
R1 has multiple sub-interfaces - one physical interface that can be attached to one interface of another router at any time, and also form an EIGRP neighborship. This instance I will connect R1 and R2 but using multiple IP's to demonstrate that neighborship is formed on both interfaces.
Here is R1
R1#show ip int brie
Interface IP-Address OK? Method Status Protocol
FastEthernet0/0 unassigned YES TFTP up up
FastEthernet0/0.1 1.1.1.1 YES manual up up
FastEthernet0/0.2 2.2.2.1 YES manual up up
interface FastEthernet0/0
no ip address
duplex auto
speed auto
!
interface FastEthernet0/0.1
encapsulation dot1Q 1 native
ip address 1.1.1.1 255.255.255.0
!
interface FastEthernet0/0.2
encapsulation dot1Q 2
ip address 2.2.2.1 255.255.255.0
router eigrp 100
network 1.1.1.1 0.0.0.0
network 2.2.2.1 0.0.0.0
no auto-summary
I have connected R2 with multiple IP's exactly the same.
R2
interface FastEthernet0/0
no ip address
duplex auto
speed auto
!
interface FastEthernet0/0.1
encapsulation dot1Q 1 native
ip address 1.1.1.2 255.255.255.0
!
interface FastEthernet0/0.2
encapsulation dot1Q 2
ip address 2.2.2.2 255.255.255.0
router eigrp 100
network 1.1.1.2 0.0.0.0
network 2.2.2.2 0.0.0.0
no auto-summary
See the EIGRP adjacencies here:
R1
R1#show ip eigrp neigh
IP-EIGRP neighbors for process 100
H Address Interface Hold Uptime SRTT RTO Q Seq
(sec) (ms) Cnt Num
1 2.2.2.2 Fa0/0.2 11 00:06:30 26 200 0 8
0 1.1.1.2 Fa0/0.1 11 00:07:26 27 200 0 5
R2
R2#show ip eigrp neighbors
IP-EIGRP neighbors for process 100
H Address Interface Hold Uptime SRTT RTO Q Seq
(sec) (ms) Cnt Num
1 2.2.2.1 Fa0/0.2 11 00:07:22 1281 5000 0 7
0 1.1.1.1 Fa0/0.1 14 00:08:18 35 210 0 4
In your case Router 1 (the mobile one) should match the sub-interface encapsulation and tag of the respective routers.
i.e.
R1 (dot1q tag 2 is to R2)
R1 (dot1q tag 3 is to R3)
Making sure its the same on both sides.
Hope this satisfies the requirement and helps.
If you have already tried the above, please check ip addressing is correct and that EIGRP config is also correct. And lastly, if this still doesn't work, try having one connection as native - I don't believe this should make a difference but the IOS might behave this way for odd reasons.
I just tested the above and works fine.
04-09-2014 10:50 PM
Thank you for solving my problem.
My problem was that in my non mobile routers I didn`t create Subinterfaces but instead just entered:
interface FastEthernet0/0
ip address 10.0.0.2 255.255.255.252
vlan-id dot1q 2
exit-vlan-config
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