IP Network Configuration

PROBLEMS CONFIGURING ROUTER:

Configuring IP routers is extremely complicated

Diversity of network equipment

Large number of configuration options

Interaction of configuration parameters across multiple routers

Rapid changes to network

Limited configuration tools

Severe consequences of error by manual configuration of individual routers

Router

It consists of a route processor, a switching fabric, a collection of interfaces.

Route processor construct forwarding table based on information of intradomain and interdomain routing protocol.

Route processor is identified by loopback IP addresses

Router name, {loopback IP address}, location, {interface}, {global setting}

INTERFACES:

Position in the router(indicated by interface name).

Each interface has a primary IP address and may have one or more secondary IP addresses; each IP address is associated with a particular prefix.

12.34.56.77 in prefix 12.34.56.76/30

Could associate with static routes , filters.

Router, interface name, {(IP address, IP prefix)}, capacity, queuing strategy, status (up/down),{access list}, {static route},OSPF weight

ROUTING PROTOCOLS:

STATIC ROUTE:

Provides a simple way to associate destination prefixes with edge interfaces.

The router knows to direct packets destined to some prefix to the appropriate next-hop interface.

Doesn’t ensure that the rest of the network knows how to reach this destination prefix.

Advertise static route via OSPF or iBGP.

administrative weight

BGP:

Distance Vector Protocol.

BGP advertisements are exchanged over a BGP session between routers.

iBGP[Pair of routers in the same AS can communicate].

But iBGP intoduces overhead in large backbone network.

OSPF:

Link state protocol.

OSPF routers exchange weight information and compute shortest path

Use flooding to propagate link-state update.

Length of path is defined as sum of weight

Extension for scalability:

Routing hierarchy(OSPF areas)

Each link belongs to SAME OSPF area

OSPF weight in interface section.

OSPF area in router section.

PACKET AND ROUTE FILTERS:

Packet filters

firewall

detect spoofed source IP address.

Route filter

Custom-Provider

avoids problem caused by misconfigured BGP policies in downstream routers.

Access list

IP prefix, permit/deny, {( interface, packet/route, in/out)}

ROUTER CONFIGURATION FILES:

Cisco’s Internet Operating System(ISO) serves as a standard for router configuration.

Language with hundreds of different commands.

Sections for interfaces, routing protocols, filters, etc.

DEPENDENCIES WITHIN A FILE:

Domain-Independent

Referencing undefined items:

Undefined access-list, route-map, …

Similar to compile error: undefined variable

Unused items:

Similar to compile warning: unused variable

DOMAIN-DEPENDENT VIOLATIONS:

Inconsistent definitions

Router level Significance (will not cause inconsistency)

Similar to local variable

For example: access-list

Network wide Significance (problematic)

Similar to External variable or function

A backbone link with interfaces on two routers: two routers should agree on the selection of an OSPF area.

TOOL TO IDENTIFY ERRORS:

Perl script that parses configuration files in Cisco IOS formation.

Populates the network model and detects possible configuration errors for AT&T Common IP Backbone.

Perl Tool:

read configuration files of all routers

read keywords for global settings and section names

forall routers

{

identify section boundaries

parse global variables

check global variables

}

foreach section in (controllers, access lists, interfaces, other filter sections, static routes, OSPF, BGP)

{

read section keywords

read customization input files

forall routers

parse section and check keywords, network model violations

forall routers

perform error checks

}

Error Types:

router1: GLOBAL ERROR: missing parameter BGP-COMMUNITY

router2: GLOBAL ERROR: incorrect parameter CEF value: ip cef

router3: ACL WARNING: default acl 6 missing

router4: ACL WARNING: default acl 7 differs from specification: deny 172.0.0.0/8

router5: CONTROLLER ERROR: missing clock sync for interface Serial2/1/0:2

router6: OSPF ERROR: ospf network 10.127.6.132/30 should either be in area 14 or 3

router7: OSPF ERROR: network: 10.126.212.0 0.0.0.3 area 2 with only one IP address 10.126.212.2

router8: OSPF ERROR: network: 10.126.12.172 0.0.0.3 area 3 with no IP address

router9: BGP ERROR: cannot resolve IP: 10.11.12.56 from ...BGP statement...