looks like either a bug or someone is possibly running a tool on you network that is constructing pkts (nmap and PackX can do that). Welchia will scan the range like that (using ARP request Broadcast) but it is usually source from a legitimate ip addy. I suggest you run a Protocol analyzer against this and see exactly what kind of data traffic this is.
In the mean time set up rate-limiting and/or acls that block anything from src addy 127.0.0.1
It might be the Welchia worm if these are ICMP packets. Welchia tries to discovers networknode via 40-bytes ICMP messages (payload contains A's only, instead of the normal 1234567890). After discoovering reachable devices it scans for open UDP ports to check if the reachable nodes are vulnerable.
Table of ContentsIntroductionVersion HistoryPossible Future
UpdatesDocuments PurposeNAT Operation in ASA 8.3+ SectionsRule Types
Network Object NATTwice NAT / Manual NATRule Types used per SectionNAT
Types used with Twice NAT / Manual NAT and Network Obje...
Table of Contents Introduction:This document describes details on how
NAT-T works. Background: ESP encrypts all critical information,
encapsulating the entire inner TCP/UDP datagram within an ESP header.
ESP is an IP protocol in the same sense that TCP an...