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...
