Re: Problem on SCTP

[Michael Tuexen]

> On 13 Jan 2017, at 10:43, Michael Tuexen <Michael.Tuexen@xxxxxxxxxxxxxxxxx> wrote:
> 
> Your router does NOT change any field in the SCTP packet, but the 
> SCTP checksum was modified from
>   Checksum: 0xbaea49e5 (not verified)
> to
>   Checksum: 0xa9a86d3f (not verified)
> At least one of these is wrong. Read the tracefiles in wireshark and
> enable checksum validation and wireshark will tell you which one is
> correct. (That is why I asked for .pcap file instead of a .txt).
> 
> My guess is that the initial checksum is correct and your box middlebox
> not only changes the destination address and ttl field and header
> checksum in the IP-header (which is expected) but also incorrectly the
> SCTP checksum. Since no field in the SCTP packet has changed, the checksum
> must be the same.
At the server have a look at the SNMP counters:
cat /proc/net/sctp/snmp
You should find a line staring with
SctpChecksumErrors
If the number reported there is positive, the node received packets
with checksum errors.

Best regards
Michael
> 
> Best regards
> Michael
>> On 13 Jan 2017, at 04:29, Sun Paul <paulrbk@xxxxxxxxx> wrote:
>> 
>> Frame 2: 98 bytes on wire (784 bits), 98 bytes captured (784 bits)
>>   Encapsulation type: Ethernet (1)
>>   Arrival Time: Jan  6, 2017 16:52:49.662321000 Malay Peninsula Standard Time
>>   [Time shift for this packet: 0.000000000 seconds]
>>   Epoch Time: 1483692769.662321000 seconds
>>   [Time delta from previous captured frame: 0.000179000 seconds]
>>   [Time delta from previous displayed frame: 0.000179000 seconds]
>>   [Time since reference or first frame: 0.000179000 seconds]
>>   Frame Number: 2
>>   Frame Length: 98 bytes (784 bits)
>>   Capture Length: 98 bytes (784 bits)
>>   [Frame is marked: False]
>>   [Frame is ignored: False]
>>   [Protocols in frame: eth:ethertype:ip:sctp]
>> Ethernet II, Src: Vmware_81:41:6b (00:50:56:81:41:6b), Dst:
>> Vmware_81:a6:a3 (00:50:56:81:a6:a3)
>>   Destination: Vmware_81:a6:a3 (00:50:56:81:a6:a3)
>>       Address: Vmware_81:a6:a3 (00:50:56:81:a6:a3)
>>       .... ..0. .... .... .... .... = LG bit: Globally unique
>> address (factory default)
>>       .... ...0 .... .... .... .... = IG bit: Individual address (unicast)
>>   Source: Vmware_81:41:6b (00:50:56:81:41:6b)
>>       Address: Vmware_81:41:6b (00:50:56:81:41:6b)
>>       .... ..0. .... .... .... .... = LG bit: Globally unique
>> address (factory default)
>>       .... ...0 .... .... .... .... = IG bit: Individual address (unicast)
>>   Type: IPv4 (0x0800)
>> Internet Protocol Version 4, Src: 192.168.206.83, Dst: 192.168.206.66
>>   0100 .... = Version: 4
>>   .... 0101 = Header Length: 20 bytes (5)
>>   Differentiated Services Field: 0x02 (DSCP: CS0, ECN: ECT(0))
>>       0000 00.. = Differentiated Services Codepoint: Default (0)
>>       .... ..10 = Explicit Congestion Notification: ECN-Capable
>> Transport codepoint '10' (2)
>>   Total Length: 84
>>   Identification: 0x0000 (0)
>>   Flags: 0x02 (Don't Fragment)
>>       0... .... = Reserved bit: Not set
>>       .1.. .... = Don't fragment: Set
>>       ..0. .... = More fragments: Not set
>>   Fragment offset: 0
>>   Time to live: 63
>>   Protocol: SCTP (132)
>>   Header checksum: 0x1d3d [validation disabled]
>>       [Good: False]
>>       [Bad: False]
>>   Source: 192.168.206.83
>>   Destination: 192.168.206.66
>>   [Source GeoIP: Unknown]
>>   [Destination GeoIP: Unknown]
>> Stream Control Transmission Protocol, Src Port: 50001 (50001), Dst
>> Port: 3868 (3868)
>>   Source port: 50001
>>   Destination port: 3868
>>   Verification tag: 0x00000000
>>   [Assocation index: 0]
>>   Checksum: 0xa9a86d3f (not verified)
>> 
>>   INIT chunk (Outbound streams: 3000, inbound streams: 3000)
>>       Chunk type: INIT (1)
>>           0... .... = Bit: Stop processing of the packet
>>           .0.. .... = Bit: Do not report
>>       Chunk flags: 0x00
>>       Chunk length: 52
>>       Initiate tag: 0xe79f40cb
>>       Advertised receiver window credit (a_rwnd): 62464
>>       Number of outbound streams: 3000
>>       Number of inbound streams: 3000
>>       Initial TSN: 176990880
>>       IPv4 address parameter (Address: 192.168.206.83)
>>           Parameter type: IPv4 address (0x0005)
>>               0... .... .... .... = Bit: Stop processing of chunk
>>               .0.. .... .... .... = Bit: Do not report
>>           Parameter length: 8
>>           IP Version 4 address: 192.168.206.83
>>       IPv4 address parameter (Address: 192.168.1.83)
>>           Parameter type: IPv4 address (0x0005)
>>               0... .... .... .... = Bit: Stop processing of chunk
>>               .0.. .... .... .... = Bit: Do not report
>>           Parameter length: 8
>>           IP Version 4 address: 192.168.1.83
>>       Supported address types parameter (Supported types: IPv6, IPv4)
>>           Parameter type: Supported address types (0x000c)
>>               0... .... .... .... = Bit: Stop processing of chunk
>>               .0.. .... .... .... = Bit: Do not report
>>           Parameter length: 8
>>           Supported address type: IPv6 address (6)
>>           Supported address type: IPv4 address (5)
>>       ECN parameter
>>           Parameter type: ECN (0x8000)
>>               1... .... .... .... = Bit: Skip parameter and continue
>> processing of the chunk
>>               .0.. .... .... .... = Bit: Do not report
>>           Parameter length: 4
>>       Forward TSN supported parameter
>>           Parameter type: Forward TSN supported (0xc000)
>>               1... .... .... .... = Bit: Skip parameter and continue
>> processing of the chunk
>>               .1.. .... .... .... = Bit: Do report
>>           Parameter length: 4
> 
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