1. Internet Control Message Protoco
Used by hosts and routers to communicate network-level information
• error reporting: unreachable host, network, port, protocol (에러 메세지)
• echo request/reply (used by ping) (리퀘스트 확인하기)
ICMP message: type, code plus first 8 bytes of IP datagram causing error
타입 11번 TTL : TTL이 0이되서 버렸다고 알려줘야 한다.
2. Traceroute & ICMP
목적지까지 가는데 정보를 찾아주는 유틸리티.
source sends sets of UDP segments to destination
• 1st set has TTL =1, 2nd set has TTL=2, etc.
datagram in nth set arrives to nth router:
• router discards datagram and sends source ICMP message (type 11,
code 0)
• ICMP message possibly includes name of router & IP address
When ICMP message arrives at source: record RTTs
3. Transition From IPv4 to IPv6
Not all routers can be upgraded simultaneously
• no “flag days”
• how will network operate with mixed IPv4 and IPv6
routers?
Tunneling: IPv6 datagram carried as payload in IPv4 datagram among IPv4 routers (“packet within a packet”)
(터널링 : IPv4와 IPv6를 같이 사용할수 있게 하는 기술)
• tunneling used extensively in other contexts (4G/5G)
