Add support for IPv6 routing header type 4

IPv6 routing header type 4 is known as Segment Routing Header (SRH).
It is used by Segment Routing (SR) to steer a packet through a
controlled set of instructions, called segments. It is described in
https://tools.ietf.org/html/draft-ietf-6man-segment-routing-header-07

An extension is added to allow tcpdump to print SRH information.

5 files changed, 46 insertions, 1 deletions

diff --git a/ip6.h b/ip6.h
index 35f12e42..9ed1499c 100644
--- a/ip6.h
+++ b/ip6.h
@@ -174,6 +174,7 @@ struct ip6_rthdr {
 
 #define IPV6_RTHDR_TYPE_0 0
 #define IPV6_RTHDR_TYPE_2 2
+#define IPV6_RTHDR_TYPE_4 4
 
 /* Type 0 Routing header */
 /* Also used for Type 2 */
@@ -186,6 +187,21 @@ struct ip6_rthdr0 {
 	struct in6_addr ip6r0_addr[1];	/* up to 23 addresses */
 };
 
+/**
+ * Type 4 Routing header
+ * known as Segment Routing Header 'SRH'
+ */
+struct ip6_srh {
+	nd_uint8_t	srh_nxt;		/* next header */
+	nd_uint8_t	srh_len;		/* length in units of 8 octets */
+	nd_uint8_t	srh_type;		/* Routing Type 4 */
+	nd_uint8_t	srh_segleft;		/* segments left */
+	nd_uint8_t	srh_last_ent;		/* Last Entry*/
+	nd_uint8_t	srh_flags;		/* Flags */
+	nd_uint16_t	srh_tag;		/* Tag */
+	struct in6_addr	srh_segments[1];	/* SRH segments list*/
+};
+
 /* Fragment header */
 struct ip6_frag {
 	nd_uint8_t  ip6f_nxt;		/* next header */
diff --git a/print-rt6.c b/print-rt6.c
index 269496aa..af74fa0a 100644
--- a/print-rt6.c
+++ b/print-rt6.c
@@ -40,6 +40,7 @@ rt6_print(netdissect_options *ndo, const u_char *bp, const u_char *bp2 _U_)
 {
 	const struct ip6_rthdr *dp;
 	const struct ip6_rthdr0 *dp0;
+	const struct ip6_srh *srh;
 	const u_char *ep;
 	u_int i, len, type;
 	const struct in6_addr *addr;
@@ -83,6 +84,33 @@ rt6_print(netdissect_options *ndo, const u_char *bp, const u_char *bp2 _U_)
 		ND_PRINT((ndo, ") "));
 		return((EXTRACT_U_1(dp0->ip6r0_len) + 1) << 3);
 		break;
+	case IPV6_RTHDR_TYPE_4:
+		srh = (const struct ip6_srh *)dp;
+		ND_PRINT((ndo, ", last-entry=%u", EXTRACT_U_1(srh->srh_last_ent)));
+
+		ND_TCHECK(srh->srh_flags);
+		if (EXTRACT_U_1(srh->srh_flags) || ndo->ndo_vflag) {
+			ND_PRINT((ndo, ", flags=0x%0x",
+				EXTRACT_U_1(srh->srh_flags)));
+		}
+
+		ND_PRINT((ndo, ", tag=%x", EXTRACT_BE_U_2(srh->srh_tag)));
+
+		if (len % 2 == 1)
+			goto trunc;
+		len >>= 1;
+		addr = &srh->srh_segments[0];
+		for (i = 0; i < len; i++) {
+			if ((const u_char *)(addr + 1) > ep)
+				goto trunc;
+
+			ND_PRINT((ndo, ", [%d]%s", i, ip6addr_string(ndo, addr)));
+			addr++;
+		}
+		/*(*/
+		ND_PRINT((ndo, ") "));
+		return((EXTRACT_U_1(srh->srh_len) + 1) << 3);
+		break;
 	default:
 		goto trunc;
 		break;
diff --git a/tests/TESTLIST b/tests/TESTLIST
index ecc93da8..1e2a8508 100644
--- a/tests/TESTLIST
+++ b/tests/TESTLIST
@@ -222,7 +222,7 @@ dnssec-vv	dnssec.pcap		dnssec-vv.out		-vv
 #IPv6 tests
 ipv6-bad-version	ipv6-bad-version.pcap 	ipv6-bad-version.out
 ipv6-routing-header	ipv6-routing-header.pcap	ipv6-routing-header.out -v
-
+ipv6-srh-ext-header	ipv6-srh-ext-header.pcap 	ipv6-srh-ext-header.out -v
 # Loopback/CTP test case
 loopback	loopback.pcap		loopback.out
 
diff --git a/tests/ipv6-srh-ext-header.out b/tests/ipv6-srh-ext-header.out
new file mode 100644
index 00000000..bca97eaa
--- /dev/null
+++ b/tests/ipv6-srh-ext-header.out
@@ -0,0 +1 @@
+IP6 (flowlabel 0x889ad, hlim 64, next-header Routing (43) payload length: 144) a:b:c:12::1 > a:b:c:2::f1:0: srcrt (len=4, type=4, segleft=1, last-entry=1, flags=0x0, tag=0, [0]a:b:c:3::d6, [1]a:b:c:2::f1:0) IP6 (flowlabel 0x889ad, hlim 64, next-header ICMPv6 (58) payload length: 64) a:b:c:12::1 > b2::2: [icmp6 sum ok] ICMP6, echo request, seq 1
diff --git a/tests/ipv6-srh-ext-header.pcap b/tests/ipv6-srh-ext-header.pcap
new file mode 100644
index 00000000..871b9e42
--- /dev/null
+++ b/tests/ipv6-srh-ext-header.pcap