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# Lab 7 - PAT & Dynamic Routing

Shrimp Co. requires enterprise-grade infrastructure for reliable operations. Implement full redundancy with dual distribution switches, OSPF dynamic routing, and PAT for scalable internet access.

Tip: Individual topology files are available in the diagrams folder on my Github

# Configuration Tasks

# Layer 2 Configuration

Ensure trunk links, VLAN databases, SVIs, and port-channels are configured to provide Layer 2 reachability between all access and distribution switches.

# 1. Configure Gateway SVIs (VRRP)

On both distribution switches (sea-mdf-dsw1 and sea-mdf-dsw2), configure SVIs with the following addresses and enable VRRP:

  • VLAN 10: 10.1.10.1 (VRRP VIP)
  • VLAN 20: 10.1.20.1 (VRRP VIP)
  • VLAN 99: 10.1.99.1 (VRRP VIP)

Assign actual IPs (.2 and .3) to the switches.
Configure VRRP priority so that dsw1 is preferred for VLANs 10 & 99, and dsw2 is preferred for VLAN 20.

# 2. Enable OSPF on Routers and Distribution Switches

  • Use OSPF process ID 1 across all routing devices.
  • Use exact network statements to advertise networks into OSPF (do not summarize).
  • Advertise:
    • All point-to-point links between routers and distribution switches
    • Loopback interfaces
    • VLAN interfaces (distribution switches only)
  • Configure all interfaces in area 0.
  • Use the command passive-interface default under OSPF configuration mode. Form adjacencies only on /30 transit networks and between VLAN 99 SVIs.

# 3. Configure PAT on Routers

  • On both sea-mdf-r1 and sea-mdf-r2, configure PAT (port address translation / overload).
  • Use standard access-list 1 to specify exact source subnets for NAT/PAT.

# 4. OSPF Default Route Injection

  • Configure a static default route with a next-hop of the Volt Communications provider edge router.
  • Inject this default route into your OSPF process so that it is learned by both distribution switches.

# Success Criteria

  • VRRP
    • VLAN 10 & 99 are Master, VLAN 20 is Backup on sea-mdf-dsw1.
  • OSPF Convergence
    • Each distribution switch has three full adjacencies; each router has two.
  • SeaMart Server Reachability
    • Every host can ping SeaMart's IP address (123.123.123.123).
  • OSPF Default Route Injection
    • Default route on the distribution switches is learned dynamically via OSPF.
  • VRRP Efficiency & Security
    • Configure VRRP timers for faster failover and enable MD5 authentication.
  • OSPF Packet Capture
    • Use tcpdump on a distribution switch interface where you expect to see OSPF Hellos.
  • Name Resolution
    • Enable Linux hosts to resolve and curl seamart.com with either method you've learned so far.

# Verification Commands 

# NAT translations
show ip nat translations

# OSPF
show ip ospf neighbor
show ip ospf interface [Ethernet0/1]

# Default route in routing table
show ip route
 
# Verify VRRP
show vrrp [brief]

# OSPF
show ip ospf neighbor
show ip ospf interface [Ethernet5]
show ip ospf summary
 
# Validate HTTP reachability
curl http://123.123.123.123

# Show routed path to a destination
traceroute 123.123.123.123

# Test DNS resolution
nslookup seamart.com

# Questions to Explore

  • When designing a network, why might you choose VRRP instead of HSRP?
  • From your OSPF Hello packet capture, what information can you extract about neighbors and timers?
  • Why is your OSPF learned default route on the distribution swiches labeled differently than the others?
  • What advantages does dynamic routing like OSPF offer over static routing?