In the Internet model (TCP/IP), this is the network layer. The Internet model pre-dates bridges which are covered at the beginning of this chapter.
You can purchase wireless routers for $25. The first router was the Internet Message Processor (IMP). Those cost about $100,000.
PPP is the Point-to-Point Protocol. Usually it is a point-to-point serial connection between two routers, though sometimes a host computer may be directly connected to a router (or another host) via PPP. PPPoE is used in many DSL connections.
It’s all done with linked lists.
This is the old way.
- ip route
The Computer Science department computers operate within a subnet (152.18.69/24) of the UNC Asheville network (18.104.22.168/16).
This is how it is done today.
AS is Autonomous System.
Try out ipinfo.io.
Before slide 86
Address allocation is handled by iana and its registries, such as ARIN. Use WHOIS IP search to look up assigned network numbers.
- arp -a
Try out a MAC manufacturer look up.
- DHCP specification
- UNC Asheville Computer Science DHCP configuration
- UNC Asheville Computer Science DHCP leases
Technically, ICMP is part of IP. However, it does have its own specification.
Here are some useful common ICMP message types:
- Time Exceeded Message mtr or traceroute
- Echo and Echo Replay Message mtr or ping
Many routers are configured so that they will not pass ICMP packages. Also access to ICMP is restricted to a handful of system utilities. See Intrusion Detection FAQ: How can attacker use ICMP for reconnaissance? for examples of why this is the case.
After slide 94
Slide 98 and on
It’s pretty much all CSCI 331 from now on. Keep in mind that these functions are often performed by expensive specific-purpose routers.
- Interior distance-vector — Routing Information Protocol (RIP)
- Interior link-state — Open Shortest Path First (OSPF)
- Exterior — Border Gateway Protocol (BGP)
Extending the textbook
Unfortunately, the textbook does not cover Network Address Translation (NAT), which is widely use in home, business, and (of course) dormitory networks. The textbook also does not cover IP6, which is supposed to replace IP4 some day.
- IBM Redbook TCP/IP Tutorial and Technical Overview
- Section 3.1.7, Network Address Translation (NAT)
- Chapter 9, IP version 6
- dig unc
- IP masquerade
- Your ISP gives you one IP address
- Your router gives your home nodes distinct IP addresses within a private IP address space
- When the home node addresses a remote IP server, magic happens
- (home-IP, home-port) ⇔ (remote-IP, remote-port)
- Access to home servers can be configured with clunky router interfaces
- Network Address Translation (NAT) Tutorial from Teracom Training Institute