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I am reading through documentation which talks about "Serial network interface" something which also shows up when IOS boots.

I never see "Serial network interface" defined anywhere. If my router says 2 Serial network interface(s) what does that mean? Does it mean that those 2 Serial network interfaces can support Ethernet? What about frame relay?

nickgrim
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T. Webster
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    Holy read the manual batman. – SpacemanSpiff Mar 18 '13 at 02:11
  • @SpacemanSpiff And, just for kicks, which manual exactly should batman read? – jscott Mar 18 '13 at 02:26
  • A serial network interface is a serial port that acts as a network interface. They can be used to connect two routers back-to-back but are most commonly used to connect to either a modem or a [DSU](http://en.wikipedia.org/wiki/Data_service_unit). – David Schwartz Mar 18 '13 at 02:47
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    Since I upvoted Spiff's comment, but its apparently too vague, here's the basic router configuration manual: http://www.cisco.com/en/US/docs/routers/access/1900/software/configuration/guide/routconf_ps10538_TSD_Products_Configuration_Guide_Chapter.html – cpt_fink Mar 18 '13 at 05:13

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While not a duplicate, you should read my answer here: Why do modern routers not require clock settings anymore?

The short answer is that before Ethernet, built-in T1 interfaces, WIC cards, etc., routers connected to each other with serial ports. Usually that serial port connected the router to something like a T1 CSU/DSU or an ISDN adapter. But the port on the router was a serial port.

I am not aware of a solution to convert a serial port on a Cisco router to Ethernet. But serial ports do support most other communications protocols like T-carriers, x.25, frame relay, etc.

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longneck
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  • +1 and I would almost accept this answer, but it's still not clear how it answers my question of if ethernet, frame-relay can be used on a serial port. Put another way, how do you know the list of layer-2 protocols supported by a given interface port? – T. Webster Mar 18 '13 at 05:56
  • see my edits. you know what protocols are supported by reading the documentation. it varies from router to router. – longneck Mar 18 '13 at 10:54
  • I used to work with a 2500 series (or maybe older) that had something like that, 10mb ethernet to serial connectors, I don't think there would be much use nowadays, native adapters are much better options. – NickW Mar 18 '13 at 11:07
  • @NickW are you thinking of AUI? it looks like a serial port, but it's not. http://en.wikipedia.org/wiki/Attachment_Unit_Interface – longneck Mar 18 '13 at 12:19
  • I just may be.. it has been many a year since I used those. – NickW Mar 18 '13 at 12:22
  • @longneck AUI could be considered a serial interface by some definitions. What it is not is an asynchronous RS232 port. Probably, the serial ports on the routers under discussion aren't either (Google suggests that you will find HSSI, an ECL signalled interface that has certainly nothing to do with RS232; or "Low-Speed Serial" interfaces on Cisco gear that also seems to be very different from RS232...) – rackandboneman Mar 18 '13 at 12:48
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SNI is the term telephone company employees use to refer to the aluminium boxes commonly attached to the side of your home. It usually is a single pair of copper telephone cables that can be rewired to accommodate two or more common extension lines within the home. Its a telephone splitter...

Emery Parish
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