Cisco 1841 router FastEthernet interfaces

[coschilperoord]

Hi,

I have noticed that I can either use a straight or a cross-over cable to connect a PC or a router to a FastEthernet interface on a Cisco 1841 router. Can someone confirm these LAN interfaces do support auto-sense MDI/MDX since I am not able to find anything in the data sheets.

[sourabhagarwal]

FastEthernet interfaces in Cisco 1841 do support Auto-MDIX feature.

check this URL which have this information.

http://www.cisco.com/en/US/products/ps5854/products_data_sheet0900aecd80581fe6.html

hope it helps ... rate if it does ...

[coschilperoord]

Thanks for your reply.

I found this doc as well but I think it's only about these HWICs, correct me if I am wrong. However, I was referring to the fixed, built-in, LAN interfaces (FastEthernet's).

I have tested both a Cisco 1801 (FastEthernet0) and a Cisco 1841 (FastEthernet0/0 and 0/1) connected with a single UTP cable to an old Cisco 2501 and it looks like it doesn't matter what type of cable you use ... the cross-cable works as we all would expect, but the straight one works as well. I was just wondering whether this functionality can be found in any Cisco documentation; so far I was only able to find auto-MDIX info on HWICs and switch-ports.

Thanks.

[andrew.burns · Accepted solution]

Hi,

This doc:

http://www.cisco.com/en/US/products/ps5853/products_installation_guide_chapter09186a0080458a31.html

covers the 1800 (fixed) built-in ports, but the equivalent doc for 1800 (modular) doesn't mention mdix, although as you've seen, it's obviously supported.

HTH

Andrew.

[coschilperoord]

Hi Andrew,

Thanks. This is what I was looking for.

Table 1-1 Summary of Cisco 1800 Series Fixed-Configuration Built-In Interfaces

Autosensing function:

Eliminates the need for a crossover cable and allows the router to detect medium-dependent interface in normal mode (MDI) or medium-dependent interface in crossover mode (MDIX) in any other PC or hub with a straight-through cable or a crossover cable.

[jay77jay77 · Accepted solution]

Hi just checked having two 1841 routers connected together on fa 0/0 via a straight cable, speed auto, duplex auto but the ports never came up.

I suspect its the PC/laptop you are using that supports auto mdix.

Regards

Jay

[coschilperoord]

Hi,

You are right. It was the engineers Laptop NIC that appears to be supporting auto-MDIX.

Looks like when there is a built-in switch (all 1800 fixed models have) the built-in LAN interface also supports auto MDIX.

Regards.