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wrong frames by ports from LAYER 2 SWITCH

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'chris'
Super Advisor

wrong frames by ports from LAYER 2 SWITCH

hi

I get wrong frames from other (different) network
by LAYER 2 SWITCH from Dell.

knows someone what could be the reason ?

subnetmasks are OK
I've changed the hardware as well, but the problem still exists.

regards
chris
10 REPLIES
Ardon
Trusted Contributor

Re: wrong frames by ports from LAYER 2 SWITCH

Chris,

I would elaborate your question a bit. What are 'wrong frames'? Giants, runts? You get the 'wrong frames' on which ProCurve Switch?
A Log File of the switch (Show Tech all) would be of big help along with a detailed network topology.

Thanks, Ardon
ProCurve Networking Engineer
Ron Kinner
Honored Contributor

Re: wrong frames by ports from LAYER 2 SWITCH

If by wrong frames you mean you are getting Frame Check Sum errors then the problem is probably a duplex mismatch. One side is set to Full and the other side to Half or Auto. Make both sides the same.

Ron
Antoniov.
Honored Contributor

Re: wrong frames by ports from LAYER 2 SWITCH

Are your cables in the wall certified for 100Mbs?
May be some cable get external noise.
Can you disable autonegotiation and set manually port and PC same configuration (for example 100Mbs/Full Duplex)?

Antonio Vigliotti
Antonio Maria Vigliotti
'chris'
Super Advisor

Re: wrong frames by ports from LAYER 2 SWITCH

the example of the wrong frame:

- - - - - - - - - - - - - - - - - - - - Frame 1168 - - - - - - - - - - - - - - - - - - - -
Frame Source Destination Bytes Abs time
Summary
---------------------------------------------------------------------------------------------------------------------------------------------------------------------
1168 000C85E5BB00 000874DFBFE8 60 20.08.2004 11:22:20
TCP: D=1077 S=139 RST WIN=0
DLC: ----- DLC Header -----
DLC:
DLC: Frame 1168 arrived at 10:22:20.0247; frame size is 60 (003C hex) bytes.
DLC: Destination = Station 000874DFBFE8
DLC: Source = Station 000C85E5BB00
DLC: Ethertype = 0800 (IP)
DLC:
IP: ----- IP Header -----
IP:
IP: Version = 4, header length = 20 bytes
IP: Type of service = 00
IP: 000. .... = routine
IP: ...0 .... = normal delay
IP: .... 0... = normal throughput
IP: .... .0.. = normal reliability
IP: .... ..0. = ECT bit - transport protocol will ignore the CE bit
IP: .... ...0 = CE bit - no congestion
IP: Total length = 40 bytes
IP: Identification = 28429
IP: Flags = 4X
IP: .1.. .... = don't fragment
IP: ..0. .... = last fragment
IP: Fragment offset = 0 bytes
IP: Time to live = 126 seconds/hops
IP: Protocol = 6 (TCP)
IP: Header checksum = 74ED (correct)
IP: Source address = [10.181.1.185]
IP: Destination address = [10.20.2.63]
IP: No options
IP:
TCP: ----- TCP header -----
TCP:
TCP: Source port = 139 (NetBIOS-ssn)
TCP: Destination port = 1077
TCP: Sequence number = 765091356
TCP: Next expected Seq number= 765091356
TCP: Data offset = 20 bytes
TCP: Reserved Bits: Reserved for Future Use (Not shown in the Hex Dump)
TCP: Flags = 04
TCP: ..0. .... = (No urgent pointer)
TCP: ...0 .... = (No acknowledgment)
TCP: .... 0... = (No push)
TCP: .... .1.. = Reset
TCP: .... ..0. = (No SYN)
TCP: .... ...0 = (No FIN)
TCP: Window = 0
TCP: Checksum = A35E (correct)
TCP: Urgent pointer = 0
TCP: No TCP options
TCP:
DLC: Frame padding= 6 bytes
Antoniov.
Honored Contributor

Re: wrong frames by ports from LAYER 2 SWITCH

Hi Chris,
I can't see any error in your packet dump.
I guess your Layer 2 Switch is a router/bridge between 2 different networks; may be some component in circuit cannot work fine. You could testing MTU of circuit using ping command from a source host as follow:
ping -f -l 1472 xxx.xxx.xxx.xxx
where xxx.xxx.xxx.xxx is destination node.
The above command fails if any component form source host to target node has MTU less than 1500.
Chris, you might specify error and explain to us some info about your network topology.

Antonio Vigliotti
Antonio Maria Vigliotti
'chris'
Super Advisor

Re: wrong frames by ports from LAYER 2 SWITCH

the problem is, that source:

IP: Source address = [10.181.1.185]

is from a different network and I should never
see this address on this switch.
Antoniov.
Honored Contributor

Re: wrong frames by ports from LAYER 2 SWITCH

Chris,

the problem is, that source:
is from a different network and I should never see this address on this switch

From 10.181.1.185
type
tracert 10.20.2.63
to see route
and from 10.20.2.63
type
tracert 10.181.1.185
to see reverse route

Antonio Vigliotti


Antonio Maria Vigliotti
Ernest Ford
Trusted Contributor

Re: wrong frames by ports from LAYER 2 SWITCH

I think you're getting a little confused here - a layer 2 switch is not concerned with ip addressing, it only cares about the MAC addresses. IP comes in with layer 3 of the OSI model.

If a station on your network needs to send a packet to another station and they are both on the same network (as determined by the ip address and subnet mask) the ip stack will simply put the packet on the wire, with the appropriate source and destination, ip MAC addresses.

However if the stations are NOT on the same network (again as determined by the ip address and subnet mask) the ip stack will then put the packet on the wire, with the appropriate source and destination ip addresses, however it will use the default gateway's MAC address instead of the destination MAC address - it will of course use the correct source MAC address.

It is therefore not only possible, but exepected that you should see packets bearing ip addresses for hosts not attached to your network (as long as your network is interconnected with one or more networks) - at no time however should you see packets with MAC addresses that are not directly attached.

'chris'
Super Advisor

Re: wrong frames by ports from LAYER 2 SWITCH

hi Ernest

you mean it's normal, that I can see frames
from other (different) networks on any ports ?

greetings
chris
Ernest Ford
Trusted Contributor
Solution

Re: wrong frames by ports from LAYER 2 SWITCH

Chris,

In a nutshell - YES - as long as you are identifying "different network" by ip address.

Let me explain.

On an ethernet LAN, all communication is done at the layer 2 level, based on the MAC addresses, ip addressing never comes into play - that occurs at layer 3.

If your network has a router connecting it to another network or the internet as most do today, then all traffic to/from that other network MUST traverse your network - expect to see frames with either the source or destination ip addresses not belonging to your network.

All "foreign" traffic should show the MAC address of your default gateway or router as either the source or destination.

I can also give you a scenario in which incorrect ip network addresses can appear on a "stand alone LAN" because of an incorrect subnet mask or routing table.

Remember (at least for a network using tcp/ip) layer 2 = MAC & layer 3 = IP