4.0 VPN Technologies

4.1 Configure and verify GRE

tunneling protocol to encapsulate wide variety of packet types "virtual P2P link"
Characteristics of GRE
- protocol-type field in header - supports encapsulation of any L3 protocol
- IP protocol 47
- stateless, no flow control
- no strong security
- GRE header + tunneling IP header = at least 24 bytes of overhead

Router 2 configuration

interface Tunnel1
  ip address 192.168.0.1 255.255.255.252     !! 'inner' tunnel IP
  tunnel source Loopback0                    !! source int on R1
  tunnel destination 4.3.2.1                 !! IP of R2

Router 2 configuration

interface Tunnel1
  ip address 192.168.0.2 255.255.255.252
  tunnel source Loopback0
  tunnel destinatio 8.7.6.5

Verification

R1# show interfaces Tunnel1
Tunnel1 is up, line protocol is up
 Hardware is Tunnel
 ...
 Encapsulation TUNNEL
 Tunnel source 8.7.6.5 (Loopback0), destination 4.3.2.1
 Tunnel protocol/transport GRE/IP
 Tunnel TTl 255, Fast tunneling enabled
 Tunnel transport MTU 1476 bytes
 ...

4.2 Describe DMVPN (single hub)

combines mGRE tunnels, IPsec encryption, and NHRP
Benefits
- less configuration on hub (single mGRE tunnel)
- NHRP to support dynamic IPsec tunnels
- supports DHCP spokes
mGRE: single GRE interface can support multiple GRE tunnels
- requires NHRP to learn peer's address and build dynamic tunnels
NHRP: used by routers to determine IP of next hop
- client-sever protocol (hub = server, spokes = clients)
- client registers it's inner (tunnel) and outer (physical) addresses
- NHRP query can be used for spoke-to-spoke communication

Verifying NHRP

# show ip nhrp
192.168.0.2 255.255.255.255, tunnel 100 created 0:00:10 expire 1:59:49
  Type: dynamic Flags: authoratative             ! authoratative includes a next-hop server provided the NHRP information
  NBMA address: 10.1111.1111.1111

IPSec: provides security
- Provides 4 services
  - Confidentiality (encryption) - no eavesdropping (uses encryption)
  - Data integrity - verify data isn't changed in path (uses checksums)
  - Authentication - ensures connection with desired partner (uses IKE)
  - Antireplay protection - verify each packet is unique/not duplicated (compare packet's seq # w/ sliding window on destination - drop late/duplicate pkts)
- Authentication (PSK or certificates) / encryption - important for DMVPN
- Relies on Authentication Header (AH) protocol 51, or Encapsulating Security Protocol (ESP) protocol 50
  - ESP - encrypts original packet
  - AH - no encryption
  - AH & ESP - can operate in tunnel mode or transport mode
    - Transport mode - uses packet's original IP header, instead of an additional tunnel header. Works well when increasing packet size is an issue. (typical in client-to-site VPN)
    - Tunnel mode - encapsulates the entire packet, so encapsulated packet has a new (IPSec header). Src/Dst reflects the VPN termination devices (typical in site-to-site VPN)

Verifying IPSec

show crypto ipsec sa
 interface: GigabitEthernet0/0
 Crypto map tag: outside_map, local addr 8.7.6.5
 local ident (addr/mask/prot/port) (50.0.0.0/255.255.255.0/0/0)
 remote ident (addr/mask/prot/port) (51.0.0.0/255.255.255.0/0/0)
 current peer: 4.3.2.1
 ...
  local crypto endpt.: 8.7.6.5, remote crypto endpt.: 4.3.2.1
  ...
  inbound esp sas:
    ...
    transform: esp-3des esp-md5-hmac ,
    ...
  outbound esp sas
    ...
    transform: esp-3des esp-md5-hmac ,
    ...

4.3 Describe Easy Virtual Networking (EVN)

provides traffic separation and path isolation
- simplify L3 virtaulization
- improve support for shared services
- enhance management/troubleshooting
uses VRF-lite to simplify Layer 3 virtualization
- traditional VRF-lite requires one subinterface per VRF throughout the datapath
Use vnet trunk instead of multiple subinterfaces
Route replication improves shared services
- Traditionally - BGP with import/export is required
- Link routes from a shared VRF to several segmented VRFs
- Not dependant on BGP route target / route distriguisher
- Removes duplicate routing talbes/routes
Routing context command allows 'troubleshooting within the VRF'
- # routing-context vrf red doesn't require 'VRF' to be specified in commands
- R1%red# show ip route short for R1# show ip route vrf red