Wireshark mailing list archives
Re: Hex Offset Needed
From: Guy Harris <guy () alum mit edu>
Date: Wed, 3 Mar 2010 18:51:44 -0800
On Mar 3, 2010, at 6:37 PM, Martin Visser wrote:
On a serious note, is libpcap able to process that filter efficiently ( I am sure it is much better than using a display filter)
Code generated for Ethernet: (000) ldh [16] (001) jeq #0x800 jt 2 jf 16 (002) ldb [27] (003) jeq #0x6 jt 4 jf 16 (004) ldh [24] (005) jset #0x1fff jt 16 jf 6 (006) ldxb 4*([18]&0xf) (007) ldb [x + 30] (008) and #0xf0 (009) rsh #2 (010) add #8 (011) add x (012) tax (013) ldh [x + 18] (014) jeq #0x2030 jt 15 jf 16 (015) ret #65535 (016) ret #0 It's not that bad. Note, though, that it doesn't handle IPv6. The IPv4-only code for "tcp port 80" is (000) ldh [16] (001) jeq #0x800 jt 2 jf 12 (002) ldb [27] (003) jeq #0x6 jt 4 jf 12 (004) ldh [24] (005) jset #0x1fff jt 12 jf 6 (006) ldxb 4*([18]&0xf) (007) ldh [x + 18] (008) jeq #0x50 jt 11 jf 9 (009) ldh [x + 20] (010) jeq #0x50 jt 11 jf 12 (011) ret #65535 (012) ret #0 so it's only 4 more BPF instructions. ___________________________________________________________________________ Sent via: Wireshark-users mailing list <wireshark-users () wireshark org> Archives: http://www.wireshark.org/lists/wireshark-users Unsubscribe: https://wireshark.org/mailman/options/wireshark-users mailto:wireshark-users-request () wireshark org?subject=unsubscribe
Current thread:
- Hex Offset Needed Sheahan, John (Mar 01)
- Re: Hex Offset Needed Sheahan, John (Mar 01)
- Re: Hex Offset Needed Martin Visser (Mar 01)
- Re: Hex Offset Needed Sheahan, John (Mar 02)
- Re: Hex Offset Needed Abhijit Bare (Mar 03)
- Re: Hex Offset Needed Sake Blok (Mar 03)
- Re: Hex Offset Needed Martin Visser (Mar 03)
- Re: Hex Offset Needed Guy Harris (Mar 03)
- Re: Hex Offset Needed Guy Harris (Mar 03)
- Re: Hex Offset Needed Sake Blok (Mar 03)
- Re: Hex Offset Needed Martin Visser (Mar 01)
- Message not available
- Re: Hex Offset Needed Sake Blok (Mar 03)
- Re: Hex Offset Needed Sheahan, John (Mar 01)