Re: Inconsistent Ping

chrismetcalf · ‎10-26-2006

Hi all,

I have a very strange problem occuring - i currently have a 4507R hooked up to a 3548 switch. When performing a continuous ping from a host sitting off the 4507 to the 3548 vlan interface i receive a very inconsistent ping rate? ranging from 1ms to 200ms? The switches are in the same VTP domain and are connected from one building to another via a fibre link, i have looked through everything and can only notice the fact that the vlan1 interface on the 3548 is shutdown, but the vlan is active (the ping is performed on another vlan interface anyway), and the only other difference i can think of is that pvst+ is not supported by the 3548 switch (the 4507 is running a few vlans). Basically has anyone ever before suffered an inconsistent ping rate due to L2 problems? or would the problem reside at L3?

apologies if i seem a little vague, but i could write a book on what i looked through, so thought i'd keep it simple

thankyou for any help

Anand Narayana · ‎10-26-2006

Hi Chriz,

was it a flat network? if so, how may PC's? it might be due to broadcasting problem which is being produced by the PC's or a Network viruz.

if not a flat network how many vlans are there in ur network? check the fiber throughput, even that might cause the problem.

check the input/output erros CRC/FCS errors etc.

you say on 3548, vlan 1 is shutdown but active. it is not possible when an interface is down & status as active.

if possbile juz post the config if the above stuff doesn't help u.

glen.grant · ‎10-26-2006

It is not a good guage to ping a vlan interface on a switch . Ping response is low man on the totem pole when it comes to things the switch is doing thus you can see what you are seeing depending how busy the switch and or router is . It is better to ping thru the device toa device on the lan itself and this should give you a better idea of how things are operating . Also look for any physical layer issues on your connecting links and or any speed/duplex mismatches...

chrismetcalf · ‎10-26-2006

hi guys, thanks for the response

i will check for CRC/FCS errors- with regards to the vlan interface being down, and the vlan still being active, i was led to believe this was a quirk of the IOS/Switch, in that the IOS/Switch could handle many vlans but would only allow one vlan interface to be up at any one time (if i try to configure the interface to force it up, it just wont come up, but if i shut another vlan interface then force the other up it works)

i will attempt to attach a quick diagram to show what i'm dealing with here

glen, if i ping through the switch, the rate is consistent and fine, i should also explain that by inconsistent ping rate i mean thatevery 3 pings is <10ms with one or ping pings afterwards being larger (up to 200ms) then back down to 3 nice quick pings, please see below:

P:\>ping 192.168.65.245 -t

Pinging 192.168.65.245 with 32 bytes of data:

Reply from 192.168.65.245: bytes=32 time=1ms TTL=254

Reply from 192.168.65.245: bytes=32 time=18ms TTL=254

Reply from 192.168.65.245: bytes=32 time=63ms TTL=254

Reply from 192.168.65.245: bytes=32 time=1ms TTL=254

Reply from 192.168.65.245: bytes=32 time=2ms TTL=254

Reply from 192.168.65.245: bytes=32 time=39ms TTL=254

Reply from 192.168.65.245: bytes=32 time=1ms TTL=254

Reply from 192.168.65.245: bytes=32 time=15ms TTL=254

Reply from 192.168.65.245: bytes=32 time=1ms TTL=254

also all speeds match, and all duplexes match (all full duplex), all hosts connected to the 3548 are experiencing slow speeds though? all switchports are plugged in by the way

could this be a general STP issue?

if i manage to get this document attached you can see that this is actually effecting 2 switches (both 3548's) which i have boxed in red

this is getting quite perplexing for me? hope my diagram isn't too rubbish!

thankyou again, you've helped already, thanks for any extra help