Ch 6 Flashcards
IPv6 traffic class field
1 bytes
replaces DS field
version field
4 bit value
IPv4 (0100) vs IPv6 (0110)
next hop address
IP of the next router to forward the packet for that network
2 Windows commands to show routing table
route print
netstat -r
packet sizes
IPv4 - 20 bytes
IPv6 - 40 bytes
IPv6 payload length field
16 bits (2 bytes) length of data payload of packet
3 Cisco router types
Branch (ISR G2) WAN (Catalyst switches, Aggregation Services Routers) Service Provider (Carrier Routing System and 7600 routers)
in-band vs out-of-band
in-band carry user traffic and require IP addressing
out-of-band dedicated to configure, manage, and troubleshoot, don’t carry user traffic
definition of routing
the process of sending packets to hosts on a remote network
IPv6 hop limit field
8 bit (2 bytes) replaces TTL field
next header
8 bits (2 bytes) same as IPv4 protocol field indicates data payload type
HWIC
high speed WAN interface card
Basic characteristics of a IP
Connectionless
Best effort delivery
Media independent
ICMP
Internet Control Message Protocol
IPv6 extension headers EH
provide optional network layer information
placed between IPv6 header and payload
used for fragmentation, security, mobility
definition of hop
each router that a packet crosses to reach its destination
IOS command for viewing routing table
show ip route
fragmentation definition
when an intermediate device splits up a packet to forward it over a medium with a smaller MTU
routers don’t fragment IPv6 packets
default route definition
a route that device uses to send a packet to a remote network when network doesn’t match any other routes.
TTL Time to Live
1 byte
limits the lifetime of packet
each hop TTL is decremented
if 0, router sends ICMP Time Exceeded message
improvements of IPv6
longer addresses (128 bits - 16 bytes) vs (32 bits - 4 bytes)
headers have fewer fields
NAT not needed
MTU maximum transmission unit
the maximum size of the PDU that a given medium can support
data link layer tells network layer its MTU
best effort definition
packet delivery is not guaranteed
cannot retransmit undelivered or corrupt packets
function of network layer
enable the transport of data from one network to another.
boot process
- perform post and load bootstrap (ROM)
- load IOS either from flash or TFTP server. If failure, use limited IOS from ROM (hash symbols)
- load startup-config from NVRAM
gateway of last resort
default route
route that router will use if packet does not match entry in routing table
Differentiated Services (DiffServ)
1 byte
used for priority
formerly called Type of Service
DSCP Differentiated Services Code Point (6 bits)
ECN Explicit Congestion Notification (2 bits)
Four basic processes of network layer
Addressing end devices
Encapsulation (adding network layer headers)
Routing
De-encapsulation
IPv6 flow label field
20 bits (2.5 bytes) how router should handle packet
packets with the same flow field value should be handled the same
Cisco routing table abbreviations
C = directly connected network L = local interface (IP on interface on router) S= static router D = EIGRP enchanced interior gateway routing protocol O = OSPF Open Shortest Path First
3 fields used for fragmentation
Identification
Flags
Fragment offset
advanced integration module
offloads processor-intensive functions away from main CPU
IPv6 simplified header benefits
better routing efficiency
no requirement for processing checksums
more efficient extension header mechanisms
flow label field
connectionless definition
no connection with the destination is established before sending packets
the recipient is not notified in advance
the benefit is there is less overhead for IP
do not know if:
- receiver present
- packet arrived
- receiver can read the packet
Cisco types of memory
RAM - routing table, arp table, running config, packet buffer
NVRAM - startup config file
Flash - IOS files
ROM - POST, limited IOS (backup), firmware for boot
of unique addresses
IPv4 - 4.2 billion
IPv6 - 340 undecillion (10^36)
limitations of IPv4
IP address depletion
routing table expansion
lack of end-to-end connectivity (NAT hides device address)
metric
how a router decides which route to use if there are two possible routes to the same destination
represents router preference
elements of routing table
router source (how router learned network)
destination network
administrative distance
metric
next-hop address
route timestamp
outgoing interface
Protocol field
1 byte
indicates data payload type
common values:
ICMP - 1
TCP - 6
UDP - 17
administrative distance
trustworthiness of router
lower values mean higher trustworthiness
IPv4 - 3 fields used for validation
IHL - Internet Header Length (4 bits) Total Length (2 bytes) Header Checksum (2 bytes)
