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Fix total_length by adding 15 bytes

master
Nico Schottelius 3 years ago
parent
commit
801b4d818e
  1. 68
      doc/plan.org
  2. 4
      p4src/static-mapping.p4

68
doc/plan.org

@ -489,7 +489,7 @@ DEBUG:main:v6 reassambled=<Ether dst=00:00:0a:00:00:42 src=00:00:0a:00:00:01 ty
debugging MIGHT come from nat64 table!
***** TODO try3: re-rewrite: no packets on h3 again (2019-03-30)
***** DONE try3: re-rewrite: no packets on h3 again (2019-03-30)
p4@ubuntu:~$ ~/master-thesis/p4app/sniff-host.sh h1 static_nat64
+ cd /home/p4/master-thesis/pcap
+ host=h1
@ -525,7 +525,73 @@ p4@ubuntu:~/master-thesis/pcap$
INFO:main:unhandled reassambled=<Ether dst=33:33:ff:00:00:42 src=00:00:0a:00:00:01 type=0x86dd |<IPv6 version=6 tc=0 fl=0 plen=32 nh=ICMPv6 hlim=255 src=fe80::200:aff:fe00:1 dst=ff02::1:ff00:42 |<ICMPv6ND_NS type=Neighbor Solicitation code=0 cksum=0x37df res=0 tgt=2001:db8::42 |<ICMPv6NDOptSrcLLAddr type=1 len=1 lladdr=00:00:0a:00:00:01 |>>>> from table TABLE_V6_NETWORKS
-> checksums likely broken again due to checksum changes
-> solved, test case for verification is
#+BEGIN_SRC
p4@ubuntu:~$ python ~/master-thesis/p4app/test.py -m v6_static_mapping --debug
INFO:main:Trying to reach 10.0.0.1 (2001:db8:1::a00:1) from h1
PING 2001:db8:1::a00:1(2001:db8:1::a00:1) 56 data bytes
From 2001:db8::1 icmp_seq=1 Destination unreachable: Address unreachable
--- 2001:db8:1::a00:1 ping statistics ---
1 packets transmitted, 0 received, +1 errors, 100% packet loss, time 0ms
p4@ubuntu:~$ python ~/master-thesis/p4app/test.py -m ping6_switch --debug
INFO:main:Trying to reach 2001:db8::42 from h1
PING 2001:db8::42(2001:db8::42) 56 data bytes
64 bytes from 2001:db8::42: icmp_seq=1 ttl=64 time=6.30 ms
--- 2001:db8::42 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 6.304/6.304/6.304/0.000 ms
#+END_SRC
***** TODO try4: h3 receives packet, but length seems to be off
- Seeing frame check sequence error
- total length ipv4 = 69 (h3)
- ipv6 payload length = 64 (h1)
- comes from hdr.ipv4.totalLen = (bit<16>) hdr.ipv6.payload_length + 5;
- https://tools.ietf.org/html/rfc791:
Total Length is the length of the datagram, measured in octets,
including internet header and data.
- checksum = 0 -> offset incorrect???
- ipv4 checksum is 0
- nat64 frame length = 98 bytes
- theory: ethernet: 48+48+16 = 112 bit -> 12 bytes
- nat64: 76 bytes inside ethernet frame
- nat64: 69 bytes according to total_len
- nat64: -5 bytes = icmp4 = 64 bytes
- icmp6 == 64 bytes
- diff of 7 bytes :-)
- icmp should be:
- type+code+checksum = 4 bytes
- seq + identifier = 4 bytes
- data = variable, source is 56 bytes
- real world ping: total_length = 84, 48 bytes icmp data
- header length in both cases = 5
- identification 0 in nat64, 0x2cad in real
- flags 0 in nat64, 0x4000 (DF) in real
- ttl = 64 both
- proto = icmp both cases
- header checksum = 0 in nat64, set in real
- data is shorter in nat64, due to total_len error
- real world icmp contains time stamp data ???
- wireshark EXPECTS timestamp data in echo request! + 8 bytes
and then data
- almost fits diff 7 vs. 8
- 8 bytes in one block in wireshark
- after ipv4: 6 + 8 + 3*(16) + 2 = 64 -- wtf??
- icmp6: data == 56 bytes
- nat64 and realping4 frame == 98 bytes
****** TODO Correct IPv4 header checksum
****** TODO Correct ICMP header checksum
****** TODO Fix length issue
- Seems like total_len is too short - but why?
**** DONE Add table name support in debug messages
**** DONE Why getting IPv6 packets in
INFO:main:unhandled reassambled=<Ether dst=33:33:ff:00:00:42 src=00:00:0a:00:00:01 type=0x86dd |<IPv6 version=6 tc=0 fl=0 plen=32 nh=ICMPv6 hlim=255 src=fe80::200:aff:fe00:1 dst=ff02::1:ff00:42 |<ICMPv6ND_NS type=Neighbor Solicitation code=0 cksum=0x37df res=0 tgt=2001:db8::42 |<ICMPv6NDOptSrcLLAddr type=1 len=1 lladdr=00:00:0a:00:00:01 |>>>> from table TABLE_V6_NETWORKS

4
p4src/static-mapping.p4

@ -77,8 +77,8 @@ control MyIngress(inout headers hdr,
/* 5 is ok as long as we don't use options / padding /
anything after the destination address */
hdr.ipv4.ihl = (bit<4>) 5; // internet header length - static for us
hdr.ipv4.totalLen = (bit<16>) hdr.ipv6.payload_length + 5; // ok under above constraints
hdr.ipv4.ihl = (bit<4>) 5; // internet header length: 4*5 = 20
hdr.ipv4.totalLen = (bit<16>) hdr.ipv6.payload_length + 20; // ok under above constraints
hdr.ipv4.identification = (bit<16>) 0; // no support for fragments
hdr.ipv4.flags = (bit<3>) 0; // DF bit and more fragments, unsupported ATM

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