Add explanation for CDP checksum algorithm
diff --git a/net/net.c b/net/net.c
index 2986924..37c5fb6 100644
--- a/net/net.c
+++ b/net/net.c
@@ -829,7 +829,10 @@
}
if (len) {
leftover = (signed short)(*(const signed char *)buff);
- /* * XXX CISCO SUCKS big time! (and blows too) */
+ /* CISCO SUCKS big time! (and blows too):
+ * CDP uses the IP checksum algorithm with a twist;
+ * for the last byte it *sign* extends and sums.
+ */
result = (result & 0xffff0000) | ((result + leftover) & 0x0000ffff);
}
while (result >> 16)