How to reach the router when the router is in ROM mode ?

Hi Here is what Cisco says:

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ip default-gateway 171.55.31.1
!--- This is the default gateway when routing is disabled.
!--- For example, if the router is in boot ROM mode. -
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I also notice some documents talk about the issue like this. My Question is if the router is in boot ROM mode, how can we reach the router ? Thank you
eemoonAsked:
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JustInCaseCommented:
I am not sure what are you asking exactly, but if one of this explanations can help.
If not, could you explain with more details....

You can access router over console or you can access over LAN if router has IP address on interface and default gateway assigned.
In rommon mode you need to change register to 0x2102 with command
confreg 0x2102
(if router is somehow stuck in rommon.
and then reload router.

For you are not in ROMmon and routing is disabled  (no ip routing) you just issue
ip routing
command.

ip default-gateway is used when routing is disabled and router is acting like end device, I use it in GNS3 when testing some configurations to use router as host. Just assign ip address to interface , and assign default gateway and that's just end host device.
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eemoonAuthor Commented:
Thanks for your fast reply. The blow link is full document. but other people also have the same conclusion, ----
After we use the command -- ip default-gateway, if the router is in boot ROM mode, we still can reach the router.
but I do not know what it exactly meant and how to reach the router using the command



http://www.cisco.com/c/en/us/support/docs/dial-access/asynchronous-connections/5466-comm-server.html
this document just mentioned command ip default-gateway
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JustInCaseCommented:
What Cisco here explains is if router is stuck somehow in rommon - routing is disabled, but if you have ip default-gateway configured on router, since you know router interface ip address, and since you have default gateway configured you can access router and configure it.  
The same thing that I explained in previous post. Router is acting like host, but since default gateway is assigned, and routing is working in other parts of network, and you can still access router and configure it. If there is no ip default gateway configured the only way to access router would be over console port or from the same VLAN (subnet).
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eemoonAuthor Commented:
Thank you for your explanation. So, in no ip routing mode, we still can reach the router from different subnet remotely, right ? if so, how can we reach the router? do you think we can still use telnet on to the interface of the router ? But the ROMMON mode is acceptable to telnet ?
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JustInCaseCommented:
Yes. You can reach router by interface ip address (the one interface that is in the same subnet as default gateway).
But for telnett in rommon I did not try that yet, but Cisco obviously says it is working. I will try it and post you back. :)
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eemoonAuthor Commented:
If it is L2 switch, and vlan2(for example) ip address is 1.1.1.2, its ip default-gateway 1.1.1.1( router interface connected to the switch). If my PC is in other network 12.12.12.12, as long as I can reach 1.1.1.1, I can telnet to the switch in Rommon mode, right ?
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JustInCaseCommented:
We were talking about router. I think VLAN concept is unknown to rommon just as it is ip routing. I guess that device needs to have ip address configured on interface and that default gateway needs to be configured. But as I said I will try does it really work tomorrow and post you back, since rommon don't work in GNS3 and tomorrow I will test it on router.
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JustInCaseCommented:
I tried to access router in rommon and I could not access to router over LAN  while router was in rommon just by assigning static ip address to interface Fa4 and configure ip default-gateway (at least on Cisco 881 router).
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eemoonAuthor Commented:
Thank you anyway
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