Bgp Routing Patterns

BGP Routing Patterns

Implementing BGP routing and traffic engineering — from iBGP/eBGP design through route selection, path manipulation, anycast, and BGP security.

When to Use

• Designing BGP peering at an IXP or data center
• Implementing multi-homed internet connectivity
• Traffic engineering with BGP path manipulation
• Building anycast network services (DNS, CDN)
• Securing BGP with RPKI and BGPsec

BGP Fundamentals

BGP_TYPES = {
    'eBGP': 'External BGP — between different autonomous systems',
    'iBGP': 'Internal BGP — between routers in the same AS',
}

BGP_PATH_ATTRIBUTES = {
    'weight': 'Cisco proprietary, highest weight preferred',
    'local_pref': 'Highest local preference preferred (within AS)',
    'as_path': 'Shortest AS_PATH preferred',
    'origin': 'IGP < EGP < Incomplete',
    'med': 'Multi-Exit Discriminator — lowest preferred',
}

# BGP route manipulation
BGP_POLICY = """
route-map SET-LOCAL-PREF permit 10
 match ip address prefix-list CUSTOMER
 set local-preference 200
!

route-map PREPEND permit 10
 set as-path prepend 64501 64501 64501
!
"""

Common Pitfalls

1. Route leaks — accidentally announcing routes you shouldn't; use prefix filtering
2. BGP hijacking — malicious AS announces your prefixes; use RPKI/ROA
3. No inbound traffic engineering — can't control where traffic enters; use AS path prepending
4. iBGP full mesh — doesn't scale; use route reflectors or confederations
5. No prefix limits — peer can advertise unlimited prefixes; set max-prefix limits

Verification Checklist

• iBGP design chosen (full mesh, route reflectors, or confederations)
• Inbound and outbound prefix filters configured
• RPKI/ROA validation implemented
• max-prefix limits set on all eBGP peers
• BGP monitoring (routes received, path flaps, convergence time)
• Traffic engineering policy documented
• BGP community strategy defined