Sends network frames to MAC Addresses (media access control).
Occasionally abbreviated to the link layer.
Components
Protocols
Terminology
| routing schemes |
broadcast, unicast, multicast, ...
|
| duplex |
If traffic can be sent/received at the same time
|
| MTU |
the largest allowed frame-size (datalink) on a network.
|
| ASN |
autonomous system number - assigned to some interior gateway protocols.
|
Tools
| arp |
discovers mac addr belonging to ipv4 addr
|
| nd |
discovers mac addr belonging to ipv6 addr
|
| tcpdump |
|
Configuration
| vlan |
using one NIC/cord to share multiple connections to separate networks (ex: WAN/LAN on firewall)
|
Troubleshooting
Error Types
| Datalink Errors
|
| frame errors |
Frames received with an invalid checksum.
|
| drops |
Frames that were discarded by the netwk iface. unexpected VLAN tags, ipv6 packets when iface is not configured for ipv6.
|
| overruns |
Too much data received too quickly (before kernel can handle them). The buffer is full, so packets are dropped.
|
| collisions |
On half-duplex netwk, when 2x sides of a connection are talking at the same time.
|
Finding Errors
TX- ## packets sent
RX- ## packets received
*-OK ## correctly recceived frames
*-ERR ## incorrect packets received
*-DRP ## packets dropped at this interface
*-OVR ## packets this interface was unable to receive
