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update checksum code

This commit is contained in:
Nico Schottelius 2019-07-17 15:46:54 +02:00
parent 4286ad0832
commit 512fca1349
2 changed files with 47 additions and 15 deletions
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13
doc/plan.org
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@ -4596,7 +4596,6 @@ Exception in thread "AWT-EventQueue-0" java.lang.IllegalArgumentException: Windo
#+END_CENTER
Reason was a hidden window.
***
*** 2019-06-13: try using external card for packets
*** 2019-06-14: test adding table entry with ubuntu 16.04, kernel 4.15.0-51-generic
#+BEGIN_CENTER
@ -5301,6 +5300,8 @@ p4@ubuntu:~/master-thesis/bin$ mx h3 "echo V4-OK | socat - UDP:10.1.1.1:2342"
My code is +1 too high
*** 2019-07-17: continuing on wrap around issue
*** DONE 2019-07-16: understood scapy code
CLOSED: [2019-07-16 Tue 11:25]
meta.v6sum = (bit<16>) ((((tmp>>8) & 0xff)|tmp<<8) & 0xffff) ;
@ -5335,7 +5336,8 @@ Gives off-by-one in udp, sometimes!
10:08:52.626713 IP6 (hlim 64, next-header UDP (17) payload length: 14) 2001:db8:1::a00:1.51345 > 2001:db8::1.2342: [bad udp cks
*** TODO 2019-07-16: get values from P4: v6sum, v4sum and co.
*** DONE 2019-07-16: get values from P4: v6sum, v4sum and co.
CLOSED: [2019-07-16 Tue 13:15]
- v6sum = 0x9a6b
- v4sum = 0xeadd
@ -5348,7 +5350,12 @@ Gives off-by-one in udp, sometimes!
hdr.udp.checksum = 0x4a8a + 0x9a6b - 0xeadd;
Result: 0xfa18!
*** TODO 2019-07-16: debug v3.3: even positive wrap around fails!!
- hdr.udp.checksum = 0x91ef + 0x9a6b;
../p4src/actions_delta_checksum.p4(66): warning: 76890: value does not fit in 16 bits
hdr.udp.checksum = 0x91ef + 0x9a6b;
11:52:13.177826 IP6 (hlim 64, next-header UDP (17) payload length: 14)
2001:db8:1::a00:1.50705 > 2001:db8::1.2342: [bad udp cksum 0x2c5a -> 0xfc97!] UDP, length 6
** The NetPFGA saga
Problems encountered:

49
p4src/actions_delta_checksum.p4
View File

@ -1,6 +1,18 @@
#ifndef NICO_DELTA_CHECKSUM
#define NICO_DELTA_CHECKSUM
/* copied from
https://p4.org/p4-spec/docs/PSA-v1.1.0.html#appendix-internetchecksum-implementation
*/
bit<16> ones_complement_sum(in bit<16> x, in bit<16> y) {
bit<17> ret = (bit<17>) x + (bit<17>) y;
if (ret[16:16] == 1) {
ret = ret + 1;
}
return ret[15:0];
}
action v4sum() {
bit<16> tmp = 0;
@ -12,7 +24,7 @@ action v4sum() {
tmp = tmp + (bit<16>) hdr.ipv4.totalLen -20; // 16 bit
tmp = tmp + (bit<16>) hdr.ipv4.protocol; // 8 bit
meta.v4sum = tmp;
meta.v4sum = ~tmp;
}
action v6sum() {
@ -39,7 +51,7 @@ action v6sum() {
tmp = tmp + (bit<16>) hdr.ipv6.payload_length; // 16 bit
tmp = tmp + (bit<16>) hdr.ipv6.next_header; // 8 bit
meta.v6sum = tmp;
meta.v6sum = ~tmp;
}
action delta_prepare()
@ -52,28 +64,41 @@ action delta_udp_from_v4_to_v6()
{
delta_prepare();
bit<16> tmp = ~hdr.udp.checksum;
tmp = tmp + meta.v6sum;
tmp = tmp - meta.v4sum;
hdr.udp.checksum = ~tmp;
bit<16> tmp = 0;
tmp = ones_complement_sum(hdr.udp.checksum, meta.v6sum);
hdr.udp.checksum = ones_complement_sum(tmp, 0xffff - meta.v6sum);
}
action delta_tcp_from_v4_to_v6()
{
delta_prepare();
bit<16> tmp = ~hdr.tcp.checksum;
tmp = tmp + meta.v6sum;
tmp = tmp - meta.v4sum;
hdr.tcp.checksum = ~tmp;
bit<16> tmp = 0;
tmp = ones_complement_sum(hdr.tcp.checksum, meta.v6sum);
hdr.tcp.checksum = ones_complement_sum(tmp, 0xffff - meta.v6sum);
}
action delta_ipv4_from_v6_to_v4()
{
delta_prepare();
bit<16> tmp = 0;
tmp = tmp + (bit<16>) hdr.ipv4.version; /* 4 bit */
tmp = tmp + (bit<16>) hdr.ipv4.ihl; /* 4 bit */
tmp = tmp + (bit<16>) hdr.ipv4.diff_serv; /* 6 bit */
tmp = tmp + (bit<16>) hdr.ipv4.ecn; /* 2 bit */
tmp = tmp + (bit<16>) hdr.ipv4.totalLen; /* 16 bit */
tmp = tmp + (bit<16>) hdr.ipv4.identification; /* 16 bit */
tmp = tmp + (bit<16>) hdr.ipv4.flags; /* 3 bit */
/* we don't have ANY checksum, but tcp or udp: we can
base on that ones for calculating the diff for IPv4
Does NOT contain payload! -> can be done manually
tmp = tmp + (bit<16>) hdr.ipv4.fragOffset;
tmp = tmp + (bit<16>) hdr.ipv4.ttl,
tmp = tmp + (bit<16>) hdr.ipv4.protocol,
tmp = tmp + (bit<16>) hdr.ipv4.src_addr,
tmp = tmp + (bit<16>) hdr.ipv4.dst_addr
*/
hdr.ipv4.checksum = 0; /* TO BE DONE! */
}