[j-nsp] Ip header problem - G/E 1000Base-LX

[Piotr S]

Hi,
i have very strange and interesting problem with juniper g/e interface. When
i am connecting this g/e to another device (juniper or cisco) the link seems
to come up, everything looks fine but the ip layer is not working. On
juniper side i can monitor traffic and everything looks fine, but the other
side just cannot see juniper packets. After many hours of investigation (and
port monitoring) it turned out that Juniper sends ip packets with bad IP
header - the length field is set to 16 (should be 20 - beside this
everything is just fine). What is more after many request online/offline
commands it sometimes start to send wrong arp replies, well the arp reply is
correct but the source address  is incorrect (zeros on 3 octet). You can see
that in ethereal capture below.
This interface had similar problem in the past but many online/offline
requests seemd to help (for one year)
It hapened in both m10 and m20, with different software, rebooting the
router didn't change anything. It seems like it have to "come up" and then
there are no problem with it.

It looks like a magic to me, any ideas what's going on?



Bogus ip header seen in ethereal:
No.     Time        Source                Destination           Protocol
Info
      1 0.000000    JuniperN_3a:ec:bc     00:14:6a:2e:8a:c2     IP
Bogus IP header length (16, must be at least 20)

Frame 1 (98 bytes on wire, 98 bytes captured)
    Arrival Time: Mar 28, 2006 02:32:42.975550000
    Time delta from previous packet: 0.000000000 seconds
    Time since reference or first frame: 0.000000000 seconds
    Frame Number: 1
    Packet Length: 98 bytes
    Capture Length: 98 bytes
Ethernet II, Src: 00:90:69:3a:ec:bc, Dst: 00:14:6a:2e:8a:c2
    Destination: 00:14:6a:2e:8a:c2 (00:14:6a:2e:8a:c2)
    Source: 00:90:69:3a:ec:bc (JuniperN_3a:ec:bc)
    Type: IP (0x0800)
Internet Protocol
    Version: 4
    Header length: 16 bytes (bogus, must be at least 20)

0000  00 14 6a 2e 8a c2 00 90 69 3a ec bc 08 00 45 00   ..j.....i:....D.
0010  00 54 9c 49 00 00 fe 01 08 89 0a ea 00 01 0a ea   .T.I............
0020  00 02 08 00 dd 7f 8e 6a 01 00 2a 84 28 44 40 4a   .......j..*.(D at J
0030  0d 00 08 09 0a 0b 0c 0d 0e 0f 10 11 12 13 14 15   ................
0040  16 17 18 19 1a 1b 1c 1d 1e 1f 20 21 22 23 24 25   .......... !"#$%
0050  26 27 28 29 2a 2b 2c 2d 2e 2f 30 31 32 33 34 35   &'()*+,-./012345
0060  36 37                                             67


Wrong arp response:
No.     Time        Source                Destination           Protocol
Info
      8 23.090667   00:14:6a:2e:8a:c3     Broadcast             ARP      Who
has 10.1.1.1?  Tell 10.1.1.2

Ethernet II, Src: 00:14:6a:2e:8a:c3, Dst: ff:ff:ff:ff:ff:ff
    Destination: ff:ff:ff:ff:ff:ff (Broadcast)
    Source: 00:14:6a:2e:8a:c3 (00:14:6a:2e:8a:c3)
    Type: ARP (0x0806)
    Trailer: 00000000000000000000000000000000...
Address Resolution Protocol (request)
    Hardware type: Ethernet (0x0001)
    Protocol type: IP (0x0800)
    Hardware size: 6
    Protocol size: 4
    Opcode: request (0x0001)
    Sender MAC address: 00:14:6a:2e:8a:c3 (00:14:6a:2e:8a:c3)
    Sender IP address: 10.1.1.2 (10.1.1.2)
    Target MAC address: 00:00:00:00:00:00 (00:00:00_00:00:00)
    Target IP address: 10.1.1.1 (10.1.1.1)

No.     Time        Source                Destination           Protocol
Info
      9 23.091781   JuniperN_3a:ec:bc     00:14:6a:2e:8a:c3     ARP
10.1.0.1 is at 00:90:69:3a:ec:bc

Ethernet II, Src: 00:90:69:3a:ec:bc, Dst: 00:14:6a:2e:8a:c3
    Destination: 00:14:6a:2e:8a:c3 (00:14:6a:2e:8a:c3)
    Source: 00:90:69:3a:ec:bc (JuniperN_3a:ec:bc)
    Type: ARP (0x0806)
    Trailer: 0A020000000000000000000000000000...
Address Resolution Protocol (reply)
    Hardware type: Ethernet (0x0001)
    Protocol type: IP (0x0800)
    Hardware size: 6
    Protocol size: 4
    Opcode: reply (0x0002)
    Sender MAC address: 00:90:69:3a:ec:bc (JuniperN_3a:ec:bc)
    Sender IP address: 10.1.0.1 (10.1.0.1)
    Target MAC address: 00:14:6a:2e:8a:c3 (00:14:6a:2e:8a:c3)
    Target IP address: 10.1.1.2 (10.1.1.2)


Regars
Piotr Szafran