Can't access switch that's in trunk mode

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Jul 10th, 2008
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I have a Cisco ASA firewall, trunked off this I have a Cisco 3750 ( which I can access via telnet from my PC.

Now off the 3750 I have trunked a 3560 ( which I can't access from my PC although I can access it via a telnet session from the 3750.

I have tried adding the "ip route" to the 3750 or ASA's IP but I still can't access.

What do you need from me fo your tom be able to help?

The IP route on the 3750 is which is our core LAN switch. The 3750 can ping this, I assume the the 3560 needs to ping this too which it can't, it's like the 3750 is not passing the traffic through. I know it is because I have lots of servers on the 3560 which I can access.


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Physically - on the 3750, which port is connected to the ASA? Which port is connected to the 3560?

Layer 2 config- on the 3750 I can only see one trunk port configured 1/0/1?

layer 3 config on both looks OK - any specific reason why for vlan 6 you are using a /16? I would probably go down to a /24


whiteford Thu, 07/10/2008 - 07:15
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3750 to ASA (trunk) = interface FastEthernet1/0/1

3750 to 3560 (trunk) = interface FastEthernet1/0/2

Yeah, i've been meaning to chage it to /24 it's more tidy, plus is it better for broadcasts?

whiteford Thu, 07/10/2008 - 07:58
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Little confused...sorry

Can you explain again,

3750 to ASA (trunk) = 3750 interface FastEthernet1/0/1

3750 to 3560 (trunk) = 3750 interface FastEthernet1/0/2

FastEthernet1/0/2 on the 3750 plugs into FastEthernet0/1 on the 3560.

Sorry - I confused myself on which device was connected to which port. Can you try the following on the 3560:-

Paste in this order.....

ip default-gateway

no ip routing

Can you also post you asa config - sanitised of course, remove anyt password's, external IP addresses etc?

whiteford Fri, 07/11/2008 - 04:24
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ip default-gateway

no ip routing

But no luck. If it helps the server that are patched into the 3560 I can get onto from my PC and access their C$ and remote desktop them, it's just managing the 3560 via SSH or telnet.

The ASA config is so huge can I just ask what part you may ned to help you?

Port 2 on the ASA is the trunk port to the 3750, so I have many virtual VLANS i suppose (not sure of the proper word), here is the config for the trunk:

interface GigabitEthernet0/2.6

vlan 6

security-level 10

ip address standby

ospf cost 10

Although I didn't configure msot of this ASA I see the standby address is the same as this switch! I did remove it but stil no luck.

whiteford Fri, 07/11/2008 - 04:52
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I can't ping the firewalls inside address of but I can ping which is the VLAN gateway on the firewall.

Just added an IP any any each way and still nothing.

Tried Packet tracer on the ASA and it beleives it can get through to the 3560: is me

"packet-tracer input inside tcp telnet"

whiteford Fri, 07/11/2008 - 05:08
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Strange thing is, I have just logged onto the ASA via telnet then type ping


Sending 5, 100-byte ICMP Echos to, timeout is 2 seconds:


Success rate is 100 percent (5/5), round-trip min/avg/max = 1/2/10 ms

whiteford Fri, 07/11/2008 - 05:41
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I have a NAT exempt from my PC's IP to /24 and ACE's from my IP (inside) to which is totally open and the opposite rule so (on the DMZ_webservers interface) to my IP on any port.

I can get to the servers on from my PC so I know the rules are working, but van't telnet to

I can only telnet to the 3560 fromthe 3750 ( and any client in that the 3560 switch.

In all honesty it should work, don't see why it does not if you say the ASA is not filtering anything.

The only other thing I could suggest - is reboot the 3560, in the past I have issues with switches not being able to reach ip addresses....and a re-load fixes all, but my switches are 3548XL's - so not really a straight comparision :o(



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