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what determines this traceroute path?

Zahan Al-Rashid
Level 1
Level 1

Hi Guys,


Got a wierd problem here, I will start by showing the IP INT BRIEF:

SPH_Bluebell_3750#show ip interface brief

Interface              IP-Address      OK? Method Status                Protocol

Vlan1                  10.100.2.55     YES NVRAM  up                    up     

Vlan69                 10.214.69.123   YES manual administratively down down   

GigabitEthernet1/0/1   unassigned      YES unset  down                  down   

GigabitEthernet1/0/2   unassigned      YES unset  up                    up     

.... etc

and now the default gateway:

SPH_Bluebell_3750#show ip default

10.214.69.126

and now the CDP neighbour:

A1_65K           1/0/25        138             R S I  WS-C6506- Gig 1/10

Now the interface betweeb this switch and the CDP is trunked:

SPH_Bluebell_3750#show run interface gigabitEthernet 1/0/25

interface GigabitEthernet1/0/25
switchport trunk encapsulation dot1q
switchport mode trunk
end

NOW THIS IS THE CONFUSING PART:

the default VLAN is 1. THe IP addresses 10.1.1.3, 10.214.69.126 and 10.100.1.249 ALL belong to the same device and this device is the A1_65k which is directly connected according to the show CDP neighbour. however when I trace route to them the give different results as shown below:

all traceroute apart from 10.100.1.249 gives the traceroute below:

SPH_Bluebell_3750#traceSPH_Bluebell_3750#traceroute 10.1.1.3

Type escape sequence to abort.
Tracing the route to 10.1.1.3

  1 10.100.2.4 0 msec 0 msec 8 msec
  2 10.100.4.25 0 msec 0 msec 9 msec
  3 10.100.4.9 0 msec *  0 msec

however traceroute below is working correctly as it is directly trunked:

SPH_Bluebell_3750#traceroute 10.100.1.249

Type escape sequence to abort.
Tracing the route to 10.100.1.249

  1 10.100.1.249 0 msec *  0 msectra

QUESTION:

I can see that traceroute works correctly for for interfaces on this switch belong to same subnet. However why is the device routing through 10.100.2.4? there is no routing table on this switch as shown below!

SPH_Bluebell_3750#show ip route
Default gateway is 10.214.69.126

Host               Gateway           Last Use    Total Uses  Interface
ICMP redirect cache is empty
SPH_Bluebell_3750#

I appreciate your assistance in figuring this out! Thanks in advance.

4 Replies 4

Robert R
Level 1
Level 1

With the SVI for vlan 69 shutdown, I'm surprised it's working at all since your default gateway is on a different vlan than the only SVI working on the switch.  Can you provide a show ip protocols, and a show run int vlan 1 from the 3750? 

Also, a show ip int brief from the 6509?

Hi Robert,


Thanks for the assist; details you requested provided below from the 10.100.2.55 (3750):

SPH_Bluebell_3750#show ip protocols

*** IP Routing is NSF aware ***

SPH_Bluebell_3750#show ip protocols
*** IP Routing is NSF aware ***

SPH_Bluebell_3750#show run interface vlan 1
Building configuration...

Current configuration : 61 bytes
!
interface Vlan1
ip address 10.100.2.55 255.255.252.0
end

      

      

THe SHOW IP INT BRIEF from 6509:

A1_65K_DS#show ip interface brief
Interface              IP-Address      OK? Method Status                Protocol
Vlan1                  10.100.1.249    YES NVRAM  up                    up     
Vlan11                 10.151.44.29    YES NVRAM  up                    up     
Vlan12                 10.151.44.61    YES NVRAM  up                    up     
Vlan13                 10.151.44.91    YES NVRAM  up                    up     
Vlan14                 10.151.44.125   YES NVRAM  up                    up     
Vlan15                 10.151.44.157   YES NVRAM  up                    up     
Vlan16                 10.151.44.189   YES NVRAM  up                    up     
Vlan17                 10.151.44.221   YES NVRAM  up                    up     
Vlan19                 10.151.46.61    YES NVRAM  up                    up     
Vlan21                 10.151.46.125   YES NVRAM  up                    up     
Vlan23                 10.151.38.60    YES NVRAM  up                    up     
Vlan29                 10.151.58.60    YES NVRAM  up                    up     
Vlan30                 10.151.46.253   YES NVRAM  up                    up     
Vlan31                 10.151.58.125   YES NVRAM  up                    up     
Vlan34                 10.214.67.124   YES NVRAM  up                    up     
Vlan37                 10.214.68.123   YES NVRAM  up                    up     
Vlan38                 192.168.17.3    YES manual up                    up     
Vlan41                 192.168.41.249  YES NVRAM  up                    up     
Vlan49                 10.151.49.123   YES manual up                    up     
Vlan56                 10.151.34.252   YES NVRAM  up                    up     
Vlan60                 172.16.1.14     YES manual administratively down down   
Vlan67                 10.151.37.249   YES NVRAM  up                    up     
Vlan69                 10.214.69.125   YES manual up                    up     
Vlan100                10.151.40.249   YES NVRAM  up                    up     
Vlan174                172.29.49.252   YES NVRAM  up                    up     
Vlan184                172.31.49.252   YES manual up                    up     
Vlan200                10.151.39.3     YES NVRAM  up                    up     
Vlan201                10.151.39.126   YES NVRAM  up                    up     
Vlan206                10.151.35.3     YES NVRAM  up                    up     
Vlan207                10.151.35.131   YES NVRAM  up                    up     
Vlan208                10.151.36.3     YES NVRAM  up                    up     
Vlan209                10.151.36.61    YES manual up                    up     
GigabitEthernet1/1     unassigned      YES unset  up                    up     
GigabitEthernet1/2     unassigned      YES unset  up                    up     
GigabitEthernet1/3     unassigned      YES unset  up                    up     
GigabitEthernet1/4     unassigned      YES unset  administratively down down   
GigabitEthernet1/5     unassigned      YES unset  administratively down down   
GigabitEthernet1/6     unassigned      YES unset  up                    up     
GigabitEthernet1/7     unassigned      YES unset  up                    up     
GigabitEthernet1/8     unassigned      YES unset  up                    up     
GigabitEthernet1/9     unassigned      YES unset  up                    up     
GigabitEthernet1/10    unassigned      YES unset  up                    up     
GigabitEthernet1/11    unassigned      YES NVRAM  administratively down down   
GigabitEthernet1/12    unassigned      YES NVRAM  administratively down down   
GigabitEthernet1/13    unassigned      YES NVRAM  administratively down down   
GigabitEthernet1/14    unassigned      YES NVRAM  administratively down down   
GigabitEthernet1/15    unassigned      YES NVRAM  administratively down down   
GigabitEthernet1/16    unassigned      YES NVRAM  administratively down down   
GigabitEthernet1/17    unassigned      YES unset  up                    up     
GigabitEthernet1/18    unassigned      YES unset  up                    up     
GigabitEthernet1/19    unassigned      YES NVRAM  administratively down down   
GigabitEthernet1/20    unassigned      YES NVRAM  administratively down down   
GigabitEthernet1/21    unassigned      YES NVRAM  down                  down   
GigabitEthernet1/22    unassigned      YES NVRAM  down                  down   
GigabitEthernet1/23    unassigned      YES NVRAM  up                    up     
GigabitEthernet1/24    unassigned      YES NVRAM  up                    up     
GigabitEthernet2/1     unassigned      YES unset  up                    up     
GigabitEthernet2/2     unassigned      YES unset  up                    up     
GigabitEthernet2/3     unassigned      YES unset  up                    up     
GigabitEthernet2/4     unassigned      YES unset  up                    up     
GigabitEthernet2/5     unassigned      YES NVRAM  administratively down down   
GigabitEthernet2/6     unassigned      YES NVRAM  administratively down down   
GigabitEthernet2/7     unassigned      YES NVRAM  administratively down down   
GigabitEthernet2/8     unassigned      YES NVRAM  administratively down down   
GigabitEthernet2/9     unassigned      YES NVRAM  administratively down down   
GigabitEthernet2/10    unassigned      YES NVRAM  administratively down down   
GigabitEthernet2/11    unassigned      YES NVRAM  administratively down down   
GigabitEthernet2/12    unassigned      YES NVRAM  administratively down down   
GigabitEthernet2/13    unassigned      YES NVRAM  administratively down down   
GigabitEthernet2/14    unassigned      YES NVRAM  administratively down down   
GigabitEthernet2/15    unassigned      YES NVRAM  administratively down down   
GigabitEthernet2/16    unassigned      YES NVRAM  administratively down down   
GigabitEthernet2/17    unassigned      YES NVRAM  administratively down down   
GigabitEthernet2/18    unassigned      YES NVRAM  administratively down down   
GigabitEthernet2/19    unassigned      YES NVRAM  administratively down down   
GigabitEthernet2/20    unassigned      YES NVRAM  administratively down down   
GigabitEthernet2/21    unassigned      YES NVRAM  administratively down down   
GigabitEthernet2/22    unassigned      YES NVRAM  administratively down down   
GigabitEthernet2/23    unassigned      YES unset  up                    up     
GigabitEthernet2/24    unassigned      YES unset  up                    up     
GigabitEthernet2/25    unassigned      YES NVRAM  administratively down down   
GigabitEthernet2/26    unassigned      YES NVRAM  administratively down down   
GigabitEthernet2/27    unassigned      YES NVRAM  administratively down down   
GigabitEthernet2/28    unassigned      YES NVRAM  administratively down down   
GigabitEthernet2/29    unassigned      YES NVRAM  administratively down down   
GigabitEthernet2/30    unassigned      YES NVRAM  administratively down down   
GigabitEthernet2/31    unassigned      YES NVRAM  administratively down down   
GigabitEthernet2/32    unassigned      YES NVRAM  administratively down down   
GigabitEthernet2/33    unassigned      YES NVRAM  administratively down down   
GigabitEthernet2/34    unassigned      YES NVRAM  administratively down down   
GigabitEthernet2/35    unassigned      YES NVRAM  administratively down down   
GigabitEthernet2/36    unassigned      YES NVRAM  administratively down down   
GigabitEthernet2/37    unassigned      YES NVRAM  administratively down down   
GigabitEthernet2/38    unassigned      YES NVRAM  administratively down down   
GigabitEthernet2/39    unassigned      YES NVRAM  administratively down down   
GigabitEthernet2/40    unassigned      YES NVRAM  administratively down down   
GigabitEthernet2/41    unassigned      YES NVRAM  administratively down down   
GigabitEthernet2/42    unassigned      YES NVRAM  administratively down down   
GigabitEthernet2/43    unassigned      YES NVRAM  administratively down down   
GigabitEthernet2/44    unassigned      YES NVRAM  administratively down down   
GigabitEthernet2/45    unassigned      YES NVRAM  administratively down down   
GigabitEthernet2/46    unassigned      YES NVRAM  administratively down down   
GigabitEthernet2/47    unassigned      YES NVRAM  administratively down down   
GigabitEthernet2/48    unassigned      YES NVRAM  administratively down down   
TenGigabitEthernet3/1  unassigned      YES unset  up                    up     
TenGigabitEthernet3/2  unassigned      YES unset  down                  down   
TenGigabitEthernet3/3  unassigned      YES unset  administratively down down   
TenGigabitEthernet3/4  unassigned      YES unset  administratively down down   
GigabitEthernet6/1     unassigned      YES NVRAM  administratively down down   
GigabitEthernet6/2     unassigned      YES unset  administratively down down   
Port-channel1          172.16.4.26     YES manual administratively down down   
Port-channel2          172.16.4.18     YES manual up                    up     
Port-channel3          unassigned      YES unset  up                    up     
Port-channel6          unassigned      YES unset  up                    up     
Port-channel75         10.100.4.6      YES NVRAM  down                  down   
Port-channel85         10.100.4.9      YES NVRAM  up                    up     
Loopback0              1.1.1.7         YES NVRAM  up                    up 

Hi Zahan,

You said that 10.1.1.3, 10.214.69.126 and 10.100.1.249 all belong to the same device, but I only see 10.100.1.249 (vlan 1 SVI) on the 6506.

where are 10.1.1.3 and 10.214.69.126?

Hi Robert;

Apologies I missed out some lines; after loopback 0 there is a 1 more line:

Loopback1              10.1.1.3        YES NVRAM  up                    up 

and the 10.214.69.126 is not an SVI but it is this switches HSRP virutal address and it is the current active one:

Interface   Grp  Pri P State   Active          Standby         Virtual IP

Vl69        69   130 P Active  local           10.214.69.124   10.214.69.126

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