[c-nsp] Are "line protocol" and LIT the same?

Sun Aug 7 10:21:52 EDT 2011

Rich,
how does Ethernet "carrier-sense mechanism" differ from "link
integrity check"? I mean aren't those two the same? A quote from
O'Reilly:

<<<<<
100BASE-TX link integrity test

The 100BASE-TX transceiver circuits (PHY) continually monitor the
receive data path for activity as a means of checking that the link is
working correctly. The signal encoding on 100BASE-TX segments sends
signals continually, even during idle periods. Therefore, activity on
the receive path is sufficient to provide a continual check of link
integrity.
>>>>>

As I understand, in case of "Link Integrity Check"(physical layer
signals) fails, the switch/router shows "line protocol is down
(notconnect)"..

regards,
martin

2011/8/2 Rich Davies <rich.davies at gmail.com>:
> I would think the switchport utilizes its carrier-sense mechanism (part of
> CSMA/CD) to see if port is in a carrier-sense state (physical connection
> layer 1).   As for the ethernet frames acting as a keepalive I am guessing
> this is a layer 2 checksum as the ethernet frames are layer 2 whereas your
> carrier sense is layer 1.
>
> Rich
>
>
> 2011/7/30 Martin T <m4rtntns at gmail.com>
>>
>> I made a following connection:
>>
>> T60[eth0] <-> [Fa0/2]WS-C2950C-24
>>
>>
>> The connection is fine:
>>
>> WS-C2950C-24#show interfaces Fa0/2 status
>>
>> Port      Name               Status       Vlan       Duplex  Speed Type
>> Fa0/2     -> T60             connected    1          a-full  a-100
>> 10/100BaseTX
>> WS-C2950C-24#
>>
>>
>> ..and at the very moment I remove the cable either from the T60 or the
>> switch, the "line protocol" in the switch will be down. Even if I
>> apply following configuration to a switch port:
>>
>> WS-C2950C-24#sh run int Fa0/2
>> Building configuration...
>>
>> Current configuration : 163 bytes
>> !
>> interface FastEthernet0/2
>>  description -> T60
>>  switchport mode access
>>  switchport nonegotiate
>>  no keepalive     !keepalive frames are disabled
>>  no cdp enable
>>  spanning-tree bpdufilter enable
>> end
>>
>> WS-C2950C-24#
>>
>> ..the line protocol of the switch port is down immediately if I
>> disconnect the cable either from the laptop or the switch. So as far
>> as I understand, keepalive frames have nothing to do with "line
>> protocol". "line protocol" status should depend on "link integrity
>> test" which means that port circuit continually sends signals- even
>> during the idle periods where there isn't any traffic on the network.
>> "link integrity test" can not be configured under software. According
>> to O'Reilly "Ethernet" this should apply to 10BASE-T, 100BASE-TX as
>> well as 1000BASE-T.
>> Anyone has an other opinion? Or confirm this? :)
>>
>>
>> regards,
>> martin
>>
>> 2011/7/28 Scott Granados <scott at granados-llc.net>:
>> > There are more measured than simple keep alives.  If you pull an
>> > interface
>> > you lose carrier, timing, frames, and other various components of the
>> > communication method in question.
>> >
>> > When you view an interface the first up indicates that the interface is
>> > enabled and the line protocol means that in a down state you're not
>> > receiving anything valid in terms of your communications protocol of
>> > choice.
>> >
>> >
>> > -----Original Message----- From: Martin T
>> > Sent: Wednesday, July 27, 2011 7:37 PM
>> > To: Lukasz Bromirski
>> > Cc: cisco-nsp at puck.nether.net
>> > Subject: Re: [c-nsp] Are "line protocol" and LIT the same?
>> >
>> > Lukasz,
>> > it looks like the default value for keepalive packet is 10s. However,
>> > if I disconnect the other end from my switch port, the line protocol
>> > will be down immediately. How to explain this? In addition, there are
>> > interfaces, which by default don't have keepaive set(for example
>> > WS-C3750G-24TS SFP interfaces). They have "Keepalive not set" under
>> > "show interfaces" output. However, they still have "line protocol is
>> > up (connected)".. How to explain this?
>> >
>> >
>> > regards,
>> > martin
>> >
>> >
>> > 2011/4/26 Lukasz Bromirski <lukasz at bromirski.net>:
>> >>
>> >> On 2011-04-26 01:11, Martin T wrote:
>> >>>
>> >>> When Cisco switch or router port is "connected", it has status "line
>> >>> protocol is up". As far as I know, this applies to all interface
>> >>> types(10BASE-T, 100BASE-TX, 1000BASE-T, 1000BASE-LX10, 1000BASE-SX etc
>> >>> with different transceivers).
>> >>> What is this "line protocol"? I always thought "line protocol" is up
>> >>> once any electrical pulses are detected by Rx. Or is "line protocol"
>> >>> strictly "link integrity test"(LIT) pulses(100-200ns of electrical
>> >>> pulses with 16ms+/-8ms interval)? Any clarification would be much
>> >>> appreciated.
>> >>
>> >> "Line protocol" for Ethernet interfaces is Ethernet frame. Cisco boxes
>> >> send Ethernet keepalive frame and when it doesn't loop back, they
>> >> declare line protocol down:
>> >>
>> >>
>> >>
>> >> http://www.cisco.com/en/US/docs/ios/12_3/interface/command/reference/int_i1g.html#wp1154231
>> >>
>> >> --
>> >> "There's no sense in being precise when |               Łukasz
>> >> Bromirski
>> >>  you don't know what you're talking     |
>> >>  jid:lbromirski at jabber.org
>> >>  about."               John von Neumann |
>> >>  http://lukasz.bromirski.net
>> >> _______________________________________________
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