Nmap Development mailing list archives
[PATCH] nping: Fix "Next-Hop MTU" in icmp "Fragmentation required" response
From: Sławomir Demeszko <s.demeszko () wireless-instruments com>
Date: Tue, 2 Feb 2016 17:08:16 +0100
Hi. When I execute a command to check MTU, for example: nping --icmp -c 1 --df --data-length=1400 8.8.8.8 where one router on the path has set MTU=1300 I get response: RCVD (0.2126s) ICMP [*.*.*.* > *.*.*.* Fragmentation required (type=3/code=4) Next-Hop-MTU=1428] IP [ttl=64 id=31483 iplen=576 ] The "Next-Hop-MTU=1428" is invalid here. It is always 28 bytes greater than length of send data and not router MTU. I checked in Wireshark and it shows proper value in response packet. MTU value is 6 and 7 byte in ICMP header, but icmppkt->data is already 4 bytes offset. Following patch resolves this. It applies to version 7.01. Signed-off-by: Sławomir Demeszko <s.demeszko () wireless-instruments com> --- libnetutil/netutil.cc | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/libnetutil/netutil.cc b/libnetutil/netutil.cc index 72d9eb2..b9757c9 100644 --- a/libnetutil/netutil.cc +++ b/libnetutil/netutil.cc @@ -2821,7 +2821,7 @@ const char *ippackethdrinfo(const u8 *packet, u32 len, int detail) { case 4: strcpy(icmptype, "Fragmentation required"); - nextmtu = (u16 *)(&(icmppkt->data[6])); + nextmtu = (u16 *)(&(icmppkt->data[2])); Snprintf(icmpfields, sizeof(icmpfields), "Next-Hop-MTU=%hu", (unsigned short) ntohs(*nextmtu)); break; -- 2.5.0 _______________________________________________ Sent through the dev mailing list https://nmap.org/mailman/listinfo/dev Archived at http://seclists.org/nmap-dev/
Current thread:
- [PATCH] nping: Fix "Next-Hop MTU" in icmp "Fragmentation required" response Sławomir Demeszko (Feb 02)
- Re: [PATCH] nping: Fix "Next-Hop MTU" in icmp "Fragmentation required" response Daniel Miller (Feb 11)