ccna
exam
course
notes: cisco Exam 640-801
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contents Page 4:
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Routing Overview |
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Routing loop checks |
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Configuring IP Routing |
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Routing Protocols |
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IP RIP |
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IGRP / EIGRP Routing |
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OSPF |
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IPX Routing |
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IP Access Lists |
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WAN Interfaces |
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Frame Relay |
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Craig Ellis Footnote on CCNA exam |
Course
notes taken by Craig Ellis(MCP)
There are 2 ways to route data;
either Static routing which is maintained by the user or Dynamic
routing which the router itself maintains the routing table.
Dynamic routing creates network overheads, as frames need to be exchanged between routers to keep the routing tables up to date.
There are 2 methods of dynamic routing:
Distance vector:
Uses HOPS as a metric. (HOPS describe the passage of a data packet between 2 network nodes i.e. 2 routers)
Routers exchange routing information frames with the distance to all known destinations
Protocols that use distance vector include:
IP and IPX RIP - IPX uses 'TICKS' as a measurement, each TICK is 1/18th of a second, but uses a HOP count before measuring TICKS - deciding best network path.
CISCO IGRP - (Interior Gateway Routing Protocol)
CISCO EIGRP - (Enhanced Interior Gateway Routing Protocol)
BGP - (Border Gateway Protocol)
Link State:
Uses a cost value as a metric - Cost values are used by routing protocols to determine the most favourable path to a destination, the lower cost = best route.
The network administrator maintains cost values.
Only advertises changes on a network
Builds database of entire network topology
Runs algorithm to determine path costs, which has a high CPU overhead
Link state protocols include:
OSPF - (Open Shortest Path First)
NLSP - (NetWare Link Services Protocol)
Routing loops occur when a route link goes down, but the router sending receives an update from a neighbouring router stating the link is available and broadcasts its finding to all.
Each time a data packet passes through a router the HOP count increases by 1 and the TTL (Time To Live) value decreases by at least 1.
To stop routing loops, the network administrator must define on the router a maximum hop count value.
RIP has a HOP count of 25, IGRP = 255 and IP + IPX = 15
SPLIT HORIZON:
Information received from a router cant be sent back to the originating router.
ROUTE POISONING:
When a network link goes down, neighbour routers advertise a (IP + IPX) HOP count of 16 (Destination Unreachable) for that network.
HOLD DOWNS:
Used to prevent regular update messages from reinstating a route that has gone down.
Routers ignore any update messages to reinstate a recently removed route for a specific period of time.
Configuring
IP Routing
Static Routing:
No updates occur on the routing network
Each interface is defined an IP address manually.
Default Routing:
Configuring a router to communicate with a 'Upstream' router i.e. Internet Service Provider
Type: IP ROUTE 0.0.0.0 0.0.0.0 131.10.11.1 (1st 2 bytes are zeros because it’s a unknown User's IP address + subnet, 3rd byte is the IP address of the 'upstream' router which ALL data goes to.)
IP CLASSLESS (this means ignore the usual IP class default values A, B, C etc.)
IGP (Interior Gateway Protocol) -
OSPF, RIP, IGRP.
EGP (Exterior Gateway Protocol) -
BGP, EIGRP, OSPF.
EGP - Used between 'Autonomous'
systems (logical grouping of routers which share network information)
EGP - ISP based networks
EGP allows non-contiguous autonomous
system domains to communicate
Neighbour RIP:
Does not broadcast tables over WAN
links
Point-to-Point serial
Frame relay
Need to configure RIP with address
of neighbour across link
Configuring RIP: from prompt
ROUTER(config)#
ROUTER RIP
ROUTER(config-router)#
NETWORK <131.107.11.0> (type in a network IP address)
NEIGHBOUR <131.107.11.2> (type in neighbours IP address)
RIP understands 'classful'
addressing only.
Passive RIP:
Stops all RIP broadcasts from being
sent out on a router interface
Router continues to receive RIP
broadcasts
This reduces network overheads
Also increased security
Configuring Passive RIP: from prompt
ROUTER(config)#
ROUTER RIP
ROUTER(config-router)#
NETWORK
PASSIVE
IP RIP Timers:
Update timer = 30 seconds
Invalid timer = 90 seconds
Hold down timer = 180 seconds
Flush timer = 270 seconds
IPX RIP Timers:
Update timer = 60 seconds
Invalid timer = 180 seconds
Hold down timer = 360 seconds
DEBUG IP RIP:
(Turns RIP debugging ON, which
checks IP frames for RIP advertisements)
UNDEBUG ALL:
(Turns off debugging)
CISCO Proprietary - All routers need
to be CISCO models otherwise they will have to be configured manually.
Rapid convergence
Reduced bandwidth - periodic
updates.
Support
for multiple active paths
Uses autonomous system numbers
Reduced
broadcast traffic
Metrics used to calculate best path
Bandwidth,
delay, reliability, load, MTU.
IGRP Timers:
Update timer: 90 seconds
Invalid timer: 270 seconds
Hold down timer: 180 seconds
Flush timer: 630 seconds
Configuring IGRP Routing:
ROUTER(config)#
ROUTER IGRP <#> (Designates the autonomous system number
between 1 and 65635)
The Autonomous System number must be
the same on the 2 routers to allow communication.
ROUTER(config-router)#
NETWORK 13.107.10.0
NEIGHBOUR 13.107.10.1
DEBUG IP IGRP EVENTS (Turns on IGRP debugging to check frames)
Uses areas to keep the route
advertisements down and kept within an area. All areas have to be directly
connected to area 0.
Usually the 1st OSPF
router on the network elects itself as the designated router (DR).
If the (DR) goes off the WAN, the
backup (DR) becomes the (DR)
If an election is held the router
with the highest IP address becomes the (DR).
OSPF is an interior routing protocol;
it can receive and send routes also to other autonomous systems.
Additional features offered by OSPF
include:
Type of Service routing (TOS)
Support for one or more metrics
Variable length subnet masks
(VLSM's)
IPX address definition:
4 byte network address: 0100 (the logical address given by
administrator)
6 byte MAC address: 112233445566
(defined by CPU)
IPX Maxium paths:
Allows multiple links between
subnets to be used for 'round robin' forwarding.
Configure IPX:
ROUTER(config)#
IPX routing
int e0
ROUTER(config-if)#
IPX network 100 encap sap
(The
default encapsulation for e0 = novell-Ether)
(The
default encapsulation for s0 = Cisco HDLC)
SHOW IPX INT (this shows all
interfaces available to use)
SHOW IPX ROUTE (this shows current
IPX set-up)
IPX Secondary and Sub-Interfaces:
IPX supports secondary and
sub-interfaces on all LAN interfaces. Only supports secondary on serial links.
Configure Secondary:
ROUTER(config-if)#
INT E0
ROUTER(config-subif)#
IPX NETWORK 2300 encap sap sec (secondary frame type supported)
Configure Sub-Interfaces:
ROUTER(config-if)#
INT E0.105 (any number for a sub-interface network)
ROUTER(config-subif)#
IPX NETWORK 2300 encap sap
A list of conditions that control
access to and from network segments.
2 types of lists:
Standard - Can only filter based on
source address only.
Extended - Can filter based on
multiple criteria (host, network, port, protocol).
Rules for access lists:
Packets are always compared to each
line of an access lit in sequential order starting from line 1.
Packets are only compared to lines
of the access list until a match is made.
There is an implicit 'deny' at the
end of each access list
If a packet does not match up to any
lines in the access list it will be discarded.
Configure standard access list:
ROUTER(config)#
ACCESS-LIST (number) (permit or deny)
(source address)
(access
list number is from 1 to 99 only)
Configure extended access list:
ROUTER(config)#
ACCESS-LIST (number) (permit or deny)
(protocol) (source address) (destination port)
(extended
access list number from 100 to 199)
i.e. ACCESS-LIST 101 PERMIT IP
100.100.10.2 0.0.0.0 100.100.10.10
(the IP subnet of 0.0.0.0 means
exact match only, if it was 255.255.255.255 then any IP number allowed)
Uses for access-lists:
Filter on ICMP only:
ROUTER(config)#
ACCESS-LIST 101 PERMIT ICMP
131.107.0.0 0.0.255.255 ANY EQ ECHO
(Implicit deny for everything else)
The access list is always 'live'
when programming on the router, its best to program offline then copy list to
the interface.
Applying access list to
interfaces:
ROUTER(config)#
INT S0
ROUTER(config-if)#
IP ACCESS-GROUP 101 IN (access group
101 set-up to become live, Inwards packets)
SHOW ACCESS-LISTS (displays all
currently active access lists)
IPX Access Lists:
(STANDARD LIST)
ROUTER(config)#
ACCESS-LIST (number) (permit or deny)
(source address) (destination address)
(Access list number from 800 to 899)
(EXTENDED LIST)
ROUTER(config)#
ACCESS-LIST (number) (permit or deny)
(protocol) (source address) (socket) (destination) (socket)
(Access list number from 900 to 999)
+ (socket: use 1109=NetBIOS or use ? for help)
IPX SAP Filters:
Controls SAP traffic, service
advertisements from file/print servers etc.
ROUTER(config)#
ACCESS-LIST (number) (permit or deny)
(source address) (service address)
Telephone services:
Demarc = your responsibility to the
point
CPE = your equipment
Local loop
CO = Central Office
DTE = Data terminating Equipment
DCE = Data Circuit Terminating
Equipment
PSE = Packet Switching Exchange
DDR = Dial on Demand
X.25 = Packet switching technology
Virtual sessions:
SVC = Switched Virtual circuit
PVC = Permanent Virtual Circuit
SDLC = Synchronous Data Link Control
Primary
Stations, Control other stations
Secondary
stations controlled by primary stations.
HDLC = High Level Data Link Control
Default
encapsulation type for CISCO serial interfaces
TRANSFER MODES:
NRM =
Normal Response Mode
ARM =
Asynchronous Response Mode
ABM =
Asynchronous Balanced Mode - LLC
LAPB =
Link Access Procedure B channel - Point to Point x.25
Operates at the physical and data
link layers of the OSI model.
Communications interface between DTE
/ DCE devices
Faster and more efficient than X.25
Assumes error checking at higher
levels
DLCI:
Data Link Connection Identifiers - (ie
MAC address for communications)
ROUTER(config)#
FRAME-RELAY INTERFACE-DLCI
(get this from your upstream
neighbour)
LMI:
ANSI,
Q933A, CISCO
(Ask for TELCO for information)
ISDN:
End to End digital, carries video
and data packets
has a higher bandwidth than
analogue.
LAPD - Link Access Protocol D
BRI - Basic Rate Isdn
2 x 64k 'b' channels and 1 x 16k 'd'
channel
Operates with CISCO models 1000,
2500, 3000 and 4000 routers
PRI:
Primary Rate Isdn
North America and Japan use: 23x16k
'b' channels and 1 64k 'd' channel
Rest of the world use: 30x16k 'b'
channels and 1 64k 'd' channel
Foot Note By Author Craig Ellis
I have been studying Cisco's CCNA
exam for sometime and I thought people like myself who are trying to learn
routing could benefit for an informative web page.
There isn't a lot to go on when
searching on the internet for CCNA exam facts but after some homework and a lot
of reading, I put together my course notes for you to look at.
If any of you appreciate the hard
work I've done then maybe you wouldn't mind contributing a small thank you to Craig Ellis via PAYPAL (ellis_craig_99@yahoo.com)
Just click on the PAYPAL icon to submit donation, thank you.
This CCNA coursework is still valid for 640-801 as per earlier CCNA exams all TCP/IP info is correct.
Address : 22 Lostock Grove, Stretford, Manchester, M32 9RP, England.
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