1. Why Replace MD5?
– MD5 is vulnerable to collision attacks,
allowing attackers to generate the same hash with different inputs.
– It is not resistant to brute-force
attacks with modern compute power.
– Officially deprecated by IETF (RFC 6151).
Impact in Cisco Protocols:
– BGP/OSPF/HSRP: Forged packets could
establish false adjacencies, hijack sessions, or disrupt routing.
– SNMPv3: MD5 + DES weakens management
plane security, allowing interception/alteration of NMS traffic.
2. Cisco Cryptography Alternatives
BGP:
– Legacy: MD5 neighbor password.
– Modern: HMAC-SHA-256 key-chains or TCP-AO
with SHA-256 (IOS-XE 17.x+, NX-OS 9.3+, IOS-XR 7.x+).
– For untrusted eBGP links: IPsec tunnel
protection.
OSPF:
– Legacy: MD5 authentication.
– Modern: OSPFv2 with HMAC-SHA-256
key-chains, OSPFv3 with IPsec ESP/AH (SHA-2).
HSRP:
– Legacy: MD5 standby authentication.
– Modern: HSRPv2/v3 with HMAC-SHA-256
key-chains.
SNMPv3:
– Legacy: MD5 authentication with DES
privacy.
– Modern: SHA authentication with
AES-128/192/256 for privacy.
3. Technical Migration Principles
– Dual Authentication: Cisco supports
key-chains with multiple keys/lifetimes (MD5 + SHA overlap).
– Protocol Dependency: Routing protocols
(BGP, OSPF, HSRP) first; management plane (SNMPv3) last.
– Platform Considerations:
*
IOS-XE: HMAC-SHA-256 since 15.1(2)SY / XE 3.7.
*
NX-OS: SHA since 7.0(3)I7; TCP-AO in 9.3+.
*
IOS-XR: SHA/TCP-AO since 6.0+.
*
ASA/FTD: SNMPv3 with SHA/AES since 9.x.
4. Example – Dual Authentication with Key-Chain
key chain BGP_KEYS
key 1
key-string OLD-MD5-KEY
cryptographic-algorithm md5
accept-lifetime 00:00:00 Jan 1 2024
infinite
send-lifetime 00:00:00 Jan 1 2024
23:59:59 Dec 31 2024
key 2
key-string NEW-SHA-KEY
cryptographic-algorithm hmac-sha-256
accept-lifetime 00:00:00 Jan 1 2024
infinite
send-lifetime 00:00:00 Jan 1 2025
infinite
– During migration: both MD5 and SHA valid.
– After cutover: disable MD5 lifetime, leaving only SHA active.
5. Risks of Not Migrating
– Vulnerable to route hijacking (BGP).
– HSRP hijack: attacker takes over virtual
IP.
– SNMPv3 downgrade: attacker reads/changes
monitoring data.
– Non-compliance with NIST SP 800-131A,
PCI-DSS, ISO 27001.
6. Operational Benefits After Migration
– Stronger compliance (SHA-256/AES-256).
– Reduced risk of cryptographic attacks.
– Consistent key rotation policies across
protocols.
– Future-proof with TCP-AO, OSPFv3 IPsec,
SNMP AES-256.
Part II – Migration Plan
1. Objectives
– Eliminate weak cryptography (MD5,
DES/3DES).
– Standardize on SHA-256 (or higher) and
AES.
– Ensure minimal disruption with staged
rollout and rollback.
2. Scope
Protocols: BGP, OSPFv2/OSPFv3, HSRP,
SNMPv3.
Platforms: IOS-XE (Cat9K, ISR, ASR1K),
NX-OS (Nexus 9K/7K/3K), IOS-XR (ASR9K, NCS), ASA/FTD.
3. Phased Migration Approach
Phase 1 – Discovery & Assessment
1. Inventory devices (OS version, crypto
configs).
2. Verify feature support for SHA-2/TCP-AO.
3. Identify OS upgrade needs.
4. Prioritize migration order: Core
(BGP/OSPF), Edge (HSRP), Management (SNMPv3).
Phase 2 – Lab Validation
1. Build lab/DR setup.
2. Validate SHA-256 configs for BGP, OSPF,
HSRP.
3. Validate OSPFv3 with IPsec ESP/AH.
4. Validate SNMPv3 with SHA/AES.
5. Test dual-auth fallback.
6. Check interoperability (multi-vendor if
applicable).
Phase 3 – Pilot Rollout
1. Select low-risk sites.
2. Implement SHA configs in parallel with
MD5.
3. Monitor adjacency/polling.
4. Rollback to MD5-only if needed.
Phase 4 – Production Migration
Step A: BGP – SHA-256 key-chain, validate,
remove MD5.
Step B: OSPF – SHA-256 key-chain, validate
adjacency, remove MD5.
Step C: HSRP – SHA-256, validate, remove
MD5.
Step D: SNMPv3 – Add SHA/AES users, migrate
NMS, remove MD5/DES users.
Phase 5 – Decommission & Hardening
1. Remove MD5/DES configs.
2. Standardize on SHA-256 and AES.
3. Update golden configs and DNAC/Prime
templates.
4. Document cryptographic standards in
LLD/HLD.
4. Rollback Plan
– Retain MD5 in parallel until stable.
– For BGP/OSPF, fallback to MD5-only
key-chain.
– For HSRP, revert to MD5 authentication.
– For SNMPv3, retain MD5/DES users until
migration confirmed.
5. Risk Mitigation
– Perform change in maintenance window.
– Stagger per protocol.
– Ensure console/OOB access.
– Monitor syslog, SNMP traps, debug logs.
6. Example Cisco Configurations
BGP (IOS-XE/NX-OS):
key chain BGP_KEYS
key 1
key-string <secure-key>
cryptographic-algorithm hmac-sha-256
!
router bgp 65000
neighbor 192.0.2.1 password keychain
BGP_KEYS
OSPFv2 (IOS-XE):
key chain OSPF_KEYS
key 1
key-string <secure-key>
cryptographic-algorithm hmac-sha-256
!
interface Gig0/0
ip ospf authentication key-chain
OSPF_KEYS
HSRP (IOS-XE):
key chain HSRP_KEYS
key 1
key-string <secure-key>
cryptographic-algorithm hmac-sha-256
!
interface Gig0/1
standby 1 ip 10.10.10.1
standby 1 authentication md5 key-chain
HSRP_KEYS
SNMPv3 (IOS-XE/NX-OS/ASA):
snmp-server group SECURE v3 priv
snmp-server user netops SECURE v3 auth sha <auth-pass> priv aes 256
<priv-pass>