Hello Adam,
Configuration register is 0x2402
... et voilà! Here is the culprit!
https://www.cisco.com/c/en/us/support/docs/routers/10000-series-routers/50421-config-register-use.html#toc-hId--612512991
Your configuration register value translates to these meanings:
- Boots default ROM software if network boot fails (0x2000)
- IP broadcast with all zeros (0x0400)
- Traditional default netboot filename (0x0002)
The correct default setting of your configuration register should be
0x2102
Once you get the chance, please change it and reload the router:
configure terminal
config-register 0x2102
end
copy run start
reload
I have also reviewed your configuration, and you have a few additional problems there that are unrelated to this issue but that would come back and bite you later.
1) You have Cisco Express Forwarding (CEF) disabled. This will decrease the throughput your router can provide, and increases the CPU load when routing packets. Please enable CEF by
configure terminal
ip cef
end
2) Your NAT configuration is partially wrong, partially incomplete.
What's incomplete: Your interface Vlan25 is marked as inside which is okay, but you don't have an interface marked as outside. This is a must without exceptions. Based on your configuration, I assume that it is
FastEthernet0/0
that should be marked as outside.
What's wrong: You have used the
ip nat source list NAT interface FastEthernet0/0 overload
command to specify how the packets should be translated. However, you missed the inside keyword from this command. Without the inside keyword, this command refers to another method and style of NAT configuration we call the NVI style, and that requires different configuration of the interfaces as well
ip nat enable instead of ip nat inside/outside
With your current configuration, the NAT would not work at all.
To fix both issues, configure:
configure terminal
no ip nat source list NAT interface FastEthernet0/0 overload
ip nat inside source list NAT interface FastEthernet0/0 overload
interface FastEthernet0/0
ip nat outside
end
3) Your
default route
is statically configured out the
Fa0/0
interface without a next hop. Pointing a static route out a multi-access interface such as Ethernet without a next hop address is a strong, resounding no. It causes an excessive ARP traffic and an excessively large ARP cache, and is completely dependent on your upstream router having Proxy ARP enabled (it is because such route causes the entire internet to be considered as directly connected on your
Fa0/0
and hence ARP-able). We already saw situations where, through this configuration, the ARP cache grew so large that it caused the router to exhaust all memory and crash - only to exhaust it again, ending in neverending repeated crashes.
I understand you configured it this way because with DHCP, you cannot assume to know the next hop address in advance. However, you do not need to configure any static
default route
if you are using DHCP. If the DHCP assigns you a
default route
it will be put into your routing table automatically without any additional configuration (with an AD of 254). If you still want to configure it statically because you want to give it a better AD, you can do it but you still need to specify the
dhcp
keyword in the static route to avoid the problems specified above.
To fix this:
configure terminal
no ip route 0.0.0.0 0.0.0.0 FastEthernet0/0
! ... and if you insist on having it configured statically because you want to lower its AD:
ip route 0.0.0.0 0.0.0.0 FastEthernet0/0 dhcp
end
Hopefully, this all will make your router work properly.
Please feel welcome to ask further!
Best regards,
Peter
