unable to trace to customer IP when using switch in between.

[nelakanna]

Dear All,

I'm facing a reachability issue when using a switch between my routers. This happened when i disconnect point to point connection between both router (R1 and R2 ).

Internet<-------R1----          --------R2------->customer  

                                |         |

                                |         |

                                 SW-1

                                |        |

                                |        |

                              R3      R4

When R1 and R2 is directly connected, i'm able to reach my customer's prefix. I learn my customer's prefix via BGP. However, when i use the switch in between, the trace stops at R1. All router's are  running Ibgp. I advertise my customer's prefix to internet via R1 and R2. There is no configuration in the switch as it is used to inter-connect between routers.

Thanks in advance.

Kanna

[pwwiddicombe]

If the switch doesn't do auto MDIX, you may have to replace the current crossover cable with 2 straight cables; plus there might be speed/duplex negotiation issues ?  You didn't specify what the switch was; or what the interface configurations are on the R1 and R2 routers.

[Cisco Freak]

Can you please more info about the devices in use?

What is the configuration of the switch? Please check if the switchport connecting R1 and R2 are part of same layer 2 VLAN.

CF

[Richard Burts]

In addition to the excellent points raised in previous posts please clarify the role of R3 and R4 in the communication between R1 and R2. Also please clarify whether the switch is just a layer 2 switch of whether it is layer 3 switch. Also clarify the connections of routers to switch, are they access ports or trunk ports and what vlans are associated with each of the interfaces.

HTH

Rick

[nelakanna]

Hi Richard,

Basically, R1 and R2 is used as upstream router and R3 and R4 will act as edge router. Due to the limited port on R3 and R4, i tried to use switch in between to connect R1 and R2. For the switch portion, i didn't place any config for the port that connecting the routers. Should i configure the ports as trunk port that allowed all vlan or it can be just a normal access port. ?

Thanks in advance.

Kanna

[nelakanna]

Hi,

Sorry for delayed response. i'm using 3750 to connect all routers. The below is the config from my switch.

*******Config for SW************

interface GigabitEthernet1/0/1
 description 1Gbps Ethernet Link to BR-1
 shutdown
 spanning-tree portfast
!
interface GigabitEthernet1/0/2
 description 1Gbps Ethernet Link to BR-2
 spanning-tree portfast
!
interface GigabitEthernet1/0/3
 description 1Gbps Ethernet Link to Edge-Router-3
 spanning-tree portfast
!
interface GigabitEthernet1/0/4
 description 1Gbps Ethernet Link to Edge-Router-4
 spanning-tree portfast

***********Config for R1 (GSR12406)*******

interface GigabitEthernet1/0
 description 1Gbps Ethernet Link to CR-SW-1
 ip address 10.10.88.241 255.255.255.240
 ip verify unicast reverse-path
 no ip redirects
 no ip directed-broadcast
 no ip proxy-arp
 ip router isis
 no ip mroute-cache
 negotiation auto
 isis circuit-type level-2-only
 hold-queue 2000 in
end

*******Config for R2  (GSR 12406)**************

interface GigabitEthernet5/3
 description 1Gbps Ethernet Link to CR-SW-1
 ip address 10.10.88.242 255.255.255.240
 no ip redirects
 no ip unreachables
 no ip directed-broadcast
 no ip proxy-arp
 ip router isis
 no ip mroute-cache
 negotiation auto

 ipv6 enable
 ipv6 router isis
 isis circuit-type level-2-only
 hold-queue 2000 in
end

*******Config for R3 (2800)****************

interface GigabitEthernet0/0
 description 1Gbps Ethernet Link to CORE-SWITCH port 3
 ip address 10.10.88.245 255.255.255.240
 no ip redirects
 no ip unreachables
 no ip proxy-arp
 ip router isis
 ip flow ingress
 ip flow egress
 duplex auto
 speed auto
 ipv6 enable
 ipv6 router isis
 isis circuit-type level-2-only
 hold-queue 2000 in
 hold-queue 2000 out
end

**********Config for R4 (7200 VXR)*************

interface GigabitEthernet0/1
 description 1Gbps Ethernet link to CORE SWITCH port 4
 ip address 10.10.88.246 255.255.255.240
 ip verify unicast reverse-path
 no ip redirects
 no ip unreachables
 no ip proxy-arp
 ip router isis
 duplex auto
 speed auto
 media-type rj45
 no negotiation auto
 ipv6 enable
 ipv6 router isis
 no cdp enable
 hold-queue 2000 in
end

********************

Thanks in advance

Kanna

[Richard Burts]

Kanna

Thank you for providing the additional information. The problem that I see is that the switch interface connecting to R1 is shutdown

interface GigabitEthernet1/0/1
 description 1Gbps Ethernet Link to BR-1
 shutdown

When you issue the no shutdown command on this interface I expect that you should have connectivity.

HTH

Rick

[nelakanna]

Hi Richard,

I have to shut GigabitEthernet1/0/1 in order to get the trace to work. Once i shut GigabitEthernet1/0/1, i bring up another direct connectivity between R1 and R2 which solve trace issue. I'm not sure whether my design is wrong or i missed out any configuration.

Secondly, when i bring up GigabitEthernet1/0/1, i notice there is a high CPU on the R1 (GSR 12406).  With this design, i try to run dual stack and try to bring down the customer R3 and R4 (Edge routers).

Thanks

Kanna

[Richard Burts]

Kanna

This is getting quite confusing. We asked about how the routers and switch are connected and you show us 4 switch ports. But then you say that you shut down one of the switch ports and use some other direct connectivity - which you have not mentioned before and which we know nothing about. How can we give you good advice when you are providing us with incomplete information in answer to our questions?

HTH

Rick

[nelakanna]

Hi Rick,

Sorry for the confusion.  Since the customer having issue with the reachability issue, i tried to connect direct between R1 and R2 to test. Eventually, it resolved the customer's issue.

So, i have a question that what cause the reachability issue  when the connection is going through switch.

Kanna