Protocols number of 50
Confidentiality & Integrity
Supports NAT, does not support PAT
Anti-Replay using Sequence Nos.
Protocol number of 51
Only Integrity; Does not support Encryption
Does not support both NAT and PAT
Anti-Replay using Sequence Nos.
Propogations of VPN Tunnels
AH Transport Mode
AH Tunnel Mode
ESP Transport Mode
ESP Tunnel Mode
The ESP header contains the following fields:
Security Parameters Index:Identifies the correct security association for the communication when used in combination with the destination address and the security protocol (AH or ESP). The receiver uses this value to determine the security association with which this packet should be identified.
Sequence Number:Provides anti-replay protection for the packet. The sequence number is a 32-bit, incrementally increasing number (starting from 1) that indicates the packet number sent over the quick mode security association for the communication. The sequence number cannot repeat for the life of the quick mode security association. The receiver checks this field to verify that a packet for a security association with this number has not already been received. If one has been received, the packet is rejected.
The ESP trailer contains the following fields:
Padding:Padding of 0 to 255 bytes is used to ensure that the encrypted payload with the padding bytes are on byte boundaries required by encryption algorithms.
Padding Length:Indicates the length of the Padding field in bytes. The receiver uses this field to remove padding bytes after the encrypted payload with the padding bytes has been decrypted.
Next Header:Identifies the type of data in the payload, such as TCP or UDP.
The ESP authentication trailer contains the following field:
Authentication Data:Contains the integrity check value (ICV), also known as the message authentication code, which is used to verify both message authentication and integrity. The receiver calculates the ICV value and checks it against this value (which is calculated by the sender) to verify integrity. The ICV is calculated over the ESP header, the payload data, and the ESP trailer.
The AH header contains the following fields:
Next Header:Identifies the IP payload by using the IP protocol ID. For example, a value of 6 represents TCP.
Length:Indicates the length of the AH header.
Security Parameters Index (SPI):Used in combination with the destination address and the security protocol (AH or ESP) to identify the correct security association for the communication. The receiver uses this value to determine with which security association the packet is identified.
Sequence Number:Provides anti-replay protection for the packet. The sequence number is a 32-bit, incrementally increasing number (starting from 1) that indicates the packet number sent over the security association for the communication. The sequence number cannot repeat for the life of the quick mode security association. The receiver checks this field to verify that a packet for a security association with this number has not already been received. If one has been received, the packet is rejected.
Authentication Data:Contains the integrity check value (ICV), also known as the message authentication code, which is used to verify both message authentication and integrity. The receiver calculates the ICV value and checks it against this value (which is calculated by the sender) to verify integrity. The ICV is calculated over the IP header, the AH header, and the IP payload.
Encryptions Protocols [Refer Introduction]
Hashing Protocols [Refer Introduction]
ISAKMP (Internet Security Association Key Management Protocol)
Uses UDP 500
Defined in RFC 2408
IKE has 2 versions
Version 1 has 2 phases
Phase 1 (ISAKMP Phase)
It has 2 Modes
Main Mode
It has 6 messages
Aggressive Mode
It has 3 messages
Message 1 (A to B): ISAKMP Policy, Vendor Id, NAT-T, NONCE, Public Key
Message 2 (B to A): The Same as above except NONCE
Message 3 (A to B): PSK/PKI (Encrypted)
Phase 2 (IKE Phase)
It has only one mode, Quick Mode
Quick Mode can operate in Tunnel and Transport Mode
It has 3 messages
Message 1 (A to B): Transport Set, Proxy ID
Message 2 (B to A): The same as above
Message 3 (A to B): Hash (QM_IDLE state)
Security Associations
They are virtual connections that are formed in between tunnels
It is used to define the set of Algorithms and the keys used for those Algorithms
Each SA will be represented by a unique SPI number
SPI is a field in AH/ESP header
It is a 32 bit field
In Phase 1, only 1 SA is formed which is bi-directional from both the sides
In Phase 2, two SAs are formed which are uni-directional from both sides
IPSec: Site to Site - Routers
Configuration Steps
Phase 1
Step 1: Configure Mirrored ACL/Crypto ACL for Interesting Traffic
(config)# access-list <#> permit host host
Step 2: Configure ISAKMP Policy
(config)# crypto isakmp policy
(config-policy)#encryption
(config-policy)# hash
(config-policy)# group
(config-policy)# authentication
(config-policy)# lifetime
Step 3: Configure ISAKMP Key
(config)# crypto isakmp key <#> address
Phase 2
Step 4: Configure Transform Set
(config)# crypto ipsec transform-set
Step 5: Configure Crypto Map
(config)# crypto map <#> ipsec-isakmp
(config-crypto-map)# set peer
(config-crypto-map)# match address
(config-crypto-map)# set transform-set
Step 6: Apply Crypto Map to an Interface
(config-if)#crypto map
To debug for Phase 1 and Phase 2. Store it in buffer without displaying logs on terminal.
Change to Transport Mode, add the following command in Step 4:
(config-tranform-set)# mode transport
Even after doing this change, the ipsec negotiation will still be done through tunnel mode if pinged from Loopback to Loopback. To overcome this we make changes to ACL.
Change to Aggressive Mode, replace the Step 3 command with these commands in R1:
(config)# crypto isakmp peer address 2.2.2.1
(config-peer)# set aggressive-mode password cisco
(config-peer)# set aggressive-mode client-endpoint ipv4-address 2.2.2.1
Similarly on R2.
The below process is for the negotiation using RSA-SIG (PKI) as authentication type
Debug Process:
After we debug, we can see the negotiation between the two peers. The first packet of the interesting traffic triggers the ISAKMP (Phase1) negotiation. Important messages are marked in BOLD and explanation in RED
R2(config)#do ping 10.1.1.1 so lo0 // Interesting Traffic
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 1.1.1.1, timeout is 2 seconds:
Packet sent with a source address of 2.2.2.2
Mar 2 16:18:42.939: ISAKMP:(0): SA request profile is (NULL) // Router tried to find any IPSec SA matching the outgoing connection but no valid SA has been found in Security Association Database (SADB)
Mar 2 16:18:42.939: ISAKMP: Created a peer struct for 20.1.1.10, peer port 500
Mar 2 16:18:42.939: ISAKMP: New peer created peer = 0x46519678 peer_handle = 0x8000000D
Mar 2 16:18:42.939: ISAKMP: Locking peer struct 0x46519678, refcount 1 for isakmp_initiator
Mar 2 16:18:42.939: ISAKMP: local port 500, remote port 500
Mar 2 16:18:42.939: ISAKMP: set new node 0 to QM_IDLE
Mar 2 16:18:42.939: ISAKMP:(0):insert sa successfully sa = 4542B818 Mar 2 16:18:42.939: ISAKMP:(0):Can not start Aggressive mode, trying Main mode. // Not an error. By default it is configured for Main Mode Mar 2 16:18:42.939: ISAKMP:(0):No pre-shared key with 20.1.1.10! // Since we are using RSA Signature, this message. If we use pre-share, this is where it would indicate so!
Mar 2 16:18:42.939: ISAKMP:(0): constructed NAT-T vendor-rfc3947 ID
Mar 2 16:18:42.939: ISAKMP:(0): constructed NAT-T vendor-07 ID
Mar 2 16:18:42.939: ISAKMP:(0): constructed NAT-T vendor-03 ID
Mar 2 16:18:42.939: ISAKMP:(0): constructed NAT-T vendor-02 ID
Mar 2 16:18:42.939: ISAKMP:(0):Input = IKE_MESG_FROM_IPSEC, IKE_SA_REQ_MM
Mar 2 16:18:42.939: ISAKMP:(0):Old State = IKE_READY New State = IKE_I_MM1
Mar 2 16:18:42.943: ISAKMP:(0): beginning Main Mode exchange Mar 2 16:18:42.943: ISAKMP:(0): sending packet to 20.1.1.10 my_port 500 peer_port 500 (I) MM_NO_STATE // Sending ISAKMP Policy to peer
Mar 2 16:18:42.943: ISAKMP:(0):Sending an IKE IPv4 Packet. Mar 2 16:18:42.943: ISAKMP (0): received packet from 20.1.1.10 dport 500 sport 500 Global (I) MM_NO_STATE// Sending ISAKMP Policy to peer
Mar 2 16:18:42.947: ISAKMP:(0):Input = IKE_MESG_FROM_PEER, IKE_MM_EXCH
Mar 2 16:18:42.947: ISAKMP:(0):Old State = IKE_I_MM1 New State = IKE_I_MM2
Mar 2 16:18:42.947: ISAKMP:(0): processing SA payload. message ID = 0
Mar 2 16:18:42.947: ISAKMP:(0): processing vendor id payload
Mar 2 16:18:42.947: ISAKMP:(0): vendor ID seems Unity/DPD but major 123 mismatch // Do not worry about this! Not an ERROR!
Mar 2 16:18:42.947: ISAKMP:(0): vendor ID is NAT-T v2
Mar 2 16:18:42.947:.!!!!
Success rate is 80 percent (4/5), round-trip min/avg/max = 1/2/4 ms
R2(config)# ISAKMP:(0): processing vendor id payload
Mar 2 16:18:42.947: ISAKMP:(0): processing IKE frag vendor id payload
Mar 2 16:18:42.947: ISAKMP:(0):Support for IKE Fragmentation not enabled
Mar 2 16:18:42.947: ISAKMP : Scanning profiles for xauth ...
Mar 2 16:18:42.947: ISAKMP:(0):Checking ISAKMP transform 1 against priority 10 policy
Mar 2 16:18:42.947: ISAKMP: encryption 3DES-CBC
Mar 2 16:18:42.947: ISAKMP: hash SHA
Mar 2 16:18:42.947: ISAKMP: default group 2
Mar 2 16:18:42.947: ISAKMP: auth RSA sig
Mar 2 16:18:42.947: ISAKMP: life type in seconds
Mar 2 16:18:42.947: ISAKMP: life duration (VPI) of 0x0 0x1 0x51 0x80
Mar 2 16:18:42.947: ISAKMP:(0):atts are acceptable. Next payload is 0
Mar 2 16:18:42.947: ISAKMP:(0):Acceptable atts:actual life: 0
Mar 2 16:18:42.947: ISAKMP:(0):Acceptable atts:life: 0
Mar 2 16:18:42.947: ISAKMP:(0):Fill atts in sa vpi_length:4
Mar 2 16:18:42.947: ISAKMP:(0):Fill atts in sa life_in_seconds:86400
Mar 2 16:18:42.947: ISAKMP:(0):Returning Actual lifetime: 86400
Mar 2 16:18:42.947: ISAKMP:(0)::Started lifetime timer: 86400.
Mar 2 16:18:42.947: ISAKMP:(0): processing vendor id payload
Mar 2 16:18:42.947: ISAKMP:(0): vendor ID seems Unity/DPD but major 123 mismatch
Mar 2 16:18:42.947: ISAKMP:(0): vendor ID is NAT-T v2
Mar 2 16:18:42.947: ISAKMP:(0): processing vendor id payload
Mar 2 16:18:42.951: ISAKMP:(0): processing IKE frag vendor id payload
Mar 2 16:18:42.951: ISAKMP:(0):Support for IKE Fragmentation not enabled
Mar 2 16:18:42.951: ISAKMP:(0):Input = IKE_MESG_INTERNAL, IKE_PROCESS_MAIN_MODE
Mar 2 16:18:42.951: ISAKMP:(0):Old State = IKE_I_MM2 New State = IKE_I_MM2
Mar 2 16:18:42.951: ISAKMP (0): constructing CERT_REQ for issuer cn=ca_server OU=cisco C=India S=Karnataka L=Bangalore
Mar 2 16:18:42.951: ISAKMP:(0): sending packet to 20.1.1.10 my_port 500 peer_port 500 (I) MM_SA_SETUP // Sending Key Exchange Information to peer
Mar 2 16:18:42.951: ISAKMP:(0):Sending an IKE IPv4 Packet.
Mar 2 16:18:42.951: ISAKMP:(0):Input = IKE_MESG_INTERNAL, IKE_PROCESS_COMPLETE
Mar 2 16:18:42.951: ISAKMP:(0):Old State = IKE_I_MM2 New State = IKE_I_MM3
Mar 2 16:18:42.955: ISAKMP (0): received packet from 20.1.1.10 dport 500 sport 500 Global (I) MM_SA_SETUP // Receive key exchange information from peer
Mar 2 16:18:42.955: ISAKMP:(0):Input = IKE_MESG_FROM_PEER, IKE_MM_EXCH
Mar 2 16:18:42.955: ISAKMP:(0):Old State = IKE_I_MM3 New State = IKE_I_MM4
Mar 2 16:18:42.959: ISAKMP:(0): processing KE payload. message ID = 0
Mar 2 16:18:43.003: ISAKMP:(0): processing NONCE payload. message ID = 0
Mar 2 16:18:43.007: ISAKMP:(1008): processing CERT_REQ payload. message ID = 0
Mar 2 16:18:43.007: ISAKMP:(1008): peer wants a CT_X509_SIGNATURE cert
Mar 2 16:18:43.007: ISAKMP:(1008): peer wants cert issued by cn=ca_server OU=cisco C=India S=Karnataka L=Bangalore
Mar 2 16:18:43.007: Choosing trustpoint CA_Server as issuer
Mar 2 16:18:43.007: ISAKMP:(1008): processing vendor id payload
Mar 2 16:18:43.007: ISAKMP:(1008): vendor ID is Unity
Mar 2 16:18:43.007: ISAKMP:(1008): processing vendor id payload
Mar 2 16:18:43.007: ISAKMP:(1008): vendor ID seems Unity/DPD but major 180 mismatch
Mar 2 16:18:43.007: ISAKMP:(1008): vendor ID is XAUTH
Mar 2 16:18:43.007: ISAKMP:(1008): processing vendor id payload
Mar 2 16:18:43.007: ISAKMP:(1008): speaking to another IOS box!
Mar 2 16:18:43.007: ISAKMP:(1008): processing vendor id payload
Mar 2 16:18:43.007: ISAKMP:(1008):vendor ID seems Unity/DPD but hash mismatch
Mar 2 16:18:43.007: ISAKMP:received payload type 20
Mar 2 16:18:43.007: ISAKMP (1008): His hash no match - this node outside NAT
Mar 2 16:18:43.007: ISAKMP:received payload type 20
Mar 2 16:18:43.007: ISAKMP (1008): No NAT Found for self or peer
Mar 2 16:18:43.007: ISAKMP:(1008):Input = IKE_MESG_INTERNAL, IKE_PROCESS_MAIN_MODE
Mar 2 16:18:43.007: ISAKMP:(1008):Old State = IKE_I_MM4 New State = IKE_I_MM4
Mar 2 16:18:43.011: ISAKMP:(1008):Send initial contact
Mar 2 16:18:43.011: ISAKMP:(1008):My ID configured as IPv4 Addr, but Addr not in Cert!
Mar 2 16:18:43.011: ISAKMP:(1008):Using FQDN as My ID
Mar 2 16:18:43.011: ISAKMP:(1008):SA is doing RSA signature authentication using id type ID_FQDN
Mar 2 16:18:43.011: ISAKMP (1008): ID payload next-payload : 6
type : 2
FQDN name : R2
protocol : 17
port : 500
length : 10
Mar 2 16:18:43.011: ISAKMP:(1008):Total payload length: 10
Mar 2 16:18:43.019: ISAKMP (1008): constructing CERT payload for hostname=R2+serialNumber=FHK1502F2H8
Mar 2 16:18:43.019: ISAKMP:(1008): using the CA_Server trustpoint's keypair to sign
Mar 2 16:18:43.035: ISAKMP:(1008): sending packet to 20.1.1.10 my_port 500 peer_port 500 (I) MM_KEY_EXCH
Mar 2 16:18:43.035: ISAKMP:(1008):Sending an IKE IPv4 Packet.
Mar 2 16:18:43.035: ISAKMP:(1008):Input = IKE_MESG_INTERNAL, IKE_PROCESS_COMPLETE
Mar 2 16:18:43.035: ISAKMP:(1008):Old State = IKE_I_MM4 New State = IKE_I_MM5
Mar 2 16:18:43.047: ISAKMP (1008): received packet from 20.1.1.10 dport 500 sport 500 Global (I) MM_KEY_EXCH
// "MM_KEY_EXCH" indicates that the peers have exchanged DH Public keys and generated a shared secret!
Mar 2 16:18:43.047: ISAKMP:(1008): processing ID payload. message ID = 0
Mar 2 16:18:43.047: ISAKMP (1008): ID payload next-payload : 6
type : 2
FQDN name : ASA1
protocol : 0
port : 0
length : 12
Mar 2 16:18:43.047: ISAKMP:(0):: peer matches *none* of the profiles // Normal Message! Not an error!
Mar 2 16:18:43.047: ISAKMP:(1008): processing CERT payload. message ID = 0
Mar 2 16:18:43.047: ISAKMP:(1008): processing a CT_X509_SIGNATURE cert
Mar 2 16:18:43.051: ISAKMP:(1008): peer's pubkey isn't cached
Mar 2 16:18:43.059: ISAKMP:(1008): Unable to get DN from certificate!
Mar 2 16:18:43.059: ISAKMP:(1008): Cert presented by peer contains no OU field.
Mar 2 16:18:43.059: ISAKMP:(0):: peer matches *none* of the profiles
Mar 2 16:18:43.063: ISAKMP:(1008): processing SIG payload. message ID = 0
Mar 2 16:18:43.067: ISAKMP:received payload type 17
Mar 2 16:18:43.067: ISAKMP:(1008): processing vendor id payload
Mar 2 16:18:43.067: ISAKMP:(1008): vendor ID is DPD
Mar 2 16:18:43.067: ISAKMP:(1008):SA authentication status: authenticated
Mar 2 16:18:43.067: ISAKMP:(1008):SA has been authenticated with 20.1.1.10
Mar 2 16:18:43.067: ISAKMP: Trying to insert a peer 40.1.1.1/20.1.1.10/500/, and inserted successfully 46519678. // SA inserted into SADB
Mar 2 16:18:43.067: ISAKMP:(1008):Input = IKE_MESG_FROM_PEER, IKE_MM_EXCH
Mar 2 16:18:43.067: ISAKMP:(1008):Old State = IKE_I_MM5 New State = IKE_I_MM6
Mar 2 16:18:43.067: ISAKMP:(1008):Input = IKE_MESG_INTERNAL, IKE_PROCESS_MAIN_MODE
Mar 2 16:18:43.067: ISAKMP:(1008):Old State = IKE_I_MM6 New State = IKE_I_MM6
Mar 2 16:18:43.071: ISAKMP:(1008):Input = IKE_MESG_INTERNAL, IKE_PROCESS_COMPLETE
Mar 2 16:18:43.071: ISAKMP:(1008):Old State = IKE_I_MM6 New State = IKE_P1_COMPLETE
Mar 2 16:18:43.071: ISAKMP:(1008):beginning Quick Mode exchange, M-ID of -1523793378
Mar 2 16:18:43.071: ISAKMP:(1008):QM Initiator gets spi
Mar 2 16:18:43.075: ISAKMP:(1008): sending packet to 20.1.1.10 my_port 500 peer_port 500 (I) QM_IDLE
Mar 2 16:18:43.075: ISAKMP:(1008):Sending an IKE IPv4 Packet.
Mar 2 16:18:43.075: ISAKMP:(1008):Node -1523793378, Input = IKE_MESG_INTERNAL, IKE_INIT_QM
Mar 2 16:18:43.075: ISAKMP:(1008):Old State = IKE_QM_READY New State = IKE_QM_I_QM1
Mar 2 16:18:43.075: ISAKMP:(1008):Input = IKE_MESG_INTERNAL, IKE_PHASE1_COMPLETE
Mar 2 16:18:43.075: ISAKMP:(1008):Old State = IKE_P1_COMPLETE New State = IKE_P1_COMPLETE
Mar 2 16:18:43.079: ISAKMP (1008): received packet from 20.1.1.10 dport 500 sport 500 Global (I) QM_IDLE // IPSec Policies
Mar 2 16:18:43.079: ISAKMP:(1008): processing HASH payload. message ID = -1523793378
Mar 2 16:18:43.079: ISAKMP:(1008): processing SA payload. message ID = -1523793378
Mar 2 16:18:43.079: ISAKMP:(1008):Checking IPSec proposal 1
Mar 2 16:18:43.079: ISAKMP: transform 1, ESP_3DES
Mar 2 16:18:43.079: ISAKMP: attributes in transform:
Mar 2 16:18:43.079: ISAKMP: SA life type in seconds
Mar 2 16:18:43.079: ISAKMP: SA life duration (basic) of 3600
Mar 2 16:18:43.079: ISAKMP: SA life type in kilobytes
Mar 2 16:18:43.079: ISAKMP: SA life duration (VPI) of 0x0 0x46 0x50 0x0
Mar 2 16:18:43.079: ISAKMP: encaps is 1 (Tunnel)
Mar 2 16:18:43.079: ISAKMP: authenticator is HMAC-SHA
Mar 2 16:18:43.079: ISAKMP:(1008):atts are acceptable. // IPSec attributes are acceptable!
Mar 2 16:18:43.079: ISAKMP:(1008): processing NONCE payload. message ID = -1523793378
Mar 2 16:18:43.079: ISAKMP:(1008): processing ID payload. message ID = -1523793378
Mar 2 16:18:43.079: ISAKMP:(1008): processing ID payload. message ID = -1523793378
Mar 2 16:18:43.083: ISAKMP:(1008): Creating IPSec SAs
Mar 2 16:18:43.083: inbound SA from 20.1.1.10 to 40.1.1.1 (f/i) 0/ 0 (proxy 1.1.1.1 to 2.2.2.2)
Mar 2 16:18:43.083: has spi 0xA9A66D46 and conn_id 0
Mar 2 16:18:43.083: lifetime of 3600 seconds
Mar 2 16:18:43.083: lifetime of 4608000 kilobytes
Mar 2 16:18:43.083: outbound SA from 40.1.1.1 to 20.1.1.10 (f/i) 0/0 (proxy 2.2.2.2 to 1.1.1.1)
Mar 2 16:18:43.083: has spi 0x2B367FB4 and conn_id 0
Mar 2 16:18:43.083: lifetime of 3600 seconds
Mar 2 16:18:43.083: lifetime of 4608000 kilobytes
Mar 2 16:18:43.083: ISAKMP:(1008): sending packet to 20.1.1.10 my_port 500 peer_port 500 (I) QM_IDLE
Mar 2 16:18:43.083: ISAKMP:(1008):Sending an IKE IPv4 Packet.
Mar 2 16:18:43.083: ISAKMP:(1008):deleting node -1523793378 error FALSE reason "No Error"
Mar 2 16:18:43.083: ISAKMP:(1008):Node -1523793378, Input = IKE_MESG_FROM_PEER, IKE_QM_EXCH
Mar 2 16:18:43.083: ISAKMP:(1008):Old State = IKE_QM_I_QM1 New State = IKE_QM_PHASE2_COMPLETE // At this point tunnels are up and ready to pass traffic!
Verification Commands
#show crypto isakmp SA
#show crypto ipsec SA
Change to Transport Mode, add the following command in Step 4:
(config-tranform-set)# mode transport
Even after doing this change, the ipsec negotiation will still be done through tunnel mode if pinged from Loopback to Loopback. To overcome this we make changes to ACL.
Change to Aggressive Mode, replace the Step 3 command with these commands in R1:
(config)# crypto isakmp peer address 2.2.2.1
(config-peer)# set aggressive-mode password cisco
(config-peer)# set aggressive-mode clien-endpoint ipv4-address 2.2.2.1
Similarly on R2.
IPSEC VPN CONFIGURATION (AGRESSIVE MODE):
R1#
access-list 101 permit ip 1.1.1.0 0.0.0.255 2.2.2.0 0.0.0.255
crypto isakmp policy 10
encr 3des
hash md5
authentication pre-share
group 2
crypto isakmp peer address 100.0.0.2
set aggressive-mode password cisco
set aggressive-mode client-endpoint ipv4-address 100.0.0.2
SPI - security parameter index - index for array of SA's - receiving router will find matching for phase 2 SA
To clear
Clear crypto isakmp
Clear crypto ipsec sa
Home Work Task
Q) Configure IPSec L2L using PSK on R1 and R2 using the following parameters
Preshare: cisco123
ISAKMP Policy
AES 256
Hash SHA
DH 2
Phase 2:
Encryption 3DES
Hash MD5
Mode : Transport
Solution: As we can see the mode required by the task is TRANSPORT. As we know transport mode is used when creating tunnels between 2 end points with traffic originating and terminating at these end points. Hence we create the ACL for the interesting traffic from R1 to R2 and vice versa. Even if we give mode transport and give the crypto ACL hosts as hosts behind the terminating end points, the negotiation will happen in tunnel mode.
AT R1:
(config)# access-list 101 permit ip host 1.1.1.1 host 2.2.2.1 // Interesting Traffic between R1 and R2
