Flashcards
Network Layer 1
Cards in this deck (18)
- 1shortcomings of switches-don't scale to large networks
blow up of routing table
-don't work across multiple link layer
-don't give much traffic controltechnology - 2routing vs forwardingrouting:process deciding which direction to go
forwarding: process of sending packet on its way - 3what kind of services does network layer provide to the transport layer?datagrams: connectionless service
virtual circuits
both implemented with store-and-forward packet switching - 4store and forwardswitching eloement has internal buffering for contention
buffer fifo - 5datagram modelpackets conain destination address
each router has forwarding table keyed by address - 6IP (internet protocol)NWL of internet uses datagrams
IPv4 carries 32 bit addresses - 7virtual circuit modelpackets only contain label to identify circuit
each router has forwarding table keyed by circuit - 8datagrams vs VCdatagrams: no setup phase, router state per destination, easier to mask
VC: packet carries short label, routing per circuit, QoS easier to add - 9longest matching prefixprefixes in table might overlap
- for each packet, find the longest(most specific) prefix that contains the destination address
-forward packet to next hop router for that prefix - 10getting IP address mapping IP to link addressDHCP & ARP
- 11DHCP addressingdiscover(broadcast address all 1's)
offer
request
ack - 12problem:node needs link layer addr. how does it get dest link address from dest IP address?ARP(address resolution protocol)
ndoe uses it to map local IP address to link layer addr(ethernet) - 13ARPsits right on top of link layerasks node with target IP to identify itself through broadcast
request->reply - 14solution for packets that are too bigfragmentation: ID,len, offset, mf
- 15MTU discoveryhost tests path with large packet
routers provide feedback tell host which size fits - 16ICMP(internet control message protocol)when router encounters error while forwarding: -sends icmp error back to ip source address
-discards problematic packet host needs to rectify - 17traceroutesends probe packets increasing ttl starting from 1
icmp errors identify routers on path - 18tunnelingtunnel carries ipv6 packets across ipv4 network
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- ETH osnet phys Flashcards on Network Layer 1, created by Francis Du on 02/12/2017.
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- Francis Du
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