Devops Network Infrastructure

DevOps Network Infrastructure

Purpose

Design networks that survive single-link, single-device, single-carrier, single-POP failures while delivering wire-rate throughput. Cover BGP for multi-homing and anycast, leaf-spine for east-west scale, EVPN/VXLAN for L2 stretch, MPLS / SD-WAN for branch, and VRRP/HSRP for L2 redundancy.

Agent Protocol

Trigger

Exact user phrases: "BGP", "anycast", "ECMP", "leaf-spine", "EVPN", "VXLAN", "MPLS", "SD-WAN", "VRRP", "HSRP", "CARP", "multi-homing", "transit", "peering", "IX", "internet exchange", "AS number", "prefix filter", "MED", "LOCAL_PREF", "DDoS scrubbing", "blackhole route", "jumbo frames", "MTU", "network fabric", "spine", "leaf", "Clos", "QoS".

Input Context

• Current topology + scale (rack count, links)
• Carrier mix (transit, peering, IX)
• Own AS number? PI / PA address space?
• Workloads (east-west heavy: storage / k8s; north-south heavy: web; both)
• Geographic POPs / regions / sites
• Compliance / latency requirements

Output Artifact

Network design with topology diagram, addressing, BGP policy, MTU plan, redundancy proof.

Response Format

Topology: {leaf-spine | hub-spoke | full-mesh}
Underlay: {BGP unnumbered | OSPF | ISIS}
Overlay: {EVPN/VXLAN | none}
North-south: {2+ transit, ≥1 IX, BGP multi-home}
Failure domains: {rack / row / pod}
MTU: {core 9216, edge 1500}

No preamble. No postamble. No explanations.

Completion Criteria

• Redundant uplinks (≥ 2 carriers; ≥ 2 fiber entries to building)
• BGP policy: prefix filter, AS path filter, RPKI ROA validation
• Anycast for stateless services where applicable
• Leaf-spine sized for non-blocking fabric (oversubscription documented)
• L2 redundancy via MLAG/VPC + VRRP/HSRP
• Consistent MTU policy across underlay
• IPv6 dual-stack
• Monitoring: BGP neighbor state, interface errors, throughput

Architecture Decision Trees

Fabric Topology Selection

Underlay Routing Protocol Comparison

BGP Route Policy Decision Tree

Ingress preference:
  Is peer at IX?
  ├── Yes → LOCAL_PREF 200 (cheaper peering)
  └── No → Is peer transit?
      ├── Yes → LOCAL_PREF 100 (paid transit)
      └── No → LOCAL_PREF 50 (backup)

Egress preference:
  Is prefix ours?
  ├── Yes → MED 100, prepend AS once
  └── No → Do we need AS prepend?
      ├── Yes → prepend 2-3 times for less-preferred path
      └── No → standard MED

Overlay Protocol Comparison

Network Vendor Comparison

Quick Start

Leaf-spine topology → BGP unnumbered underlay → EVPN/VXLAN overlay (if needed) → BGP multi-homing for north-south → Anycast for DNS/API → VRRP for L2 redundancy → MTU 9216 core → Monitoring with Prometheus + SNMP.

Core Workflow

Step 1: Pick Fabric Topology

Leaf-spine (Clos)
  All leaves connect to all spines. East-west predictable. Most modern DCs.
  Scale: add more spines/leaves; non-blocking with right oversub ratio.

Hub-spoke
  One core, many edges. Good for small / branch; bad for east-west.

Full-mesh
  All-to-all links. Only for small clusters; doesn't scale beyond ~8 nodes.

3-stage Clos (leaf-spine)        small/medium DC
5-stage Clos (super-spine added) hyperscale (1000s of racks)

        Spine-1   Spine-2   Spine-3   Spine-4
          │ │ │     │ │ │     │ │ │     │ │ │
          ╳ ╳ ╳     ╳ ╳ ╳     ╳ ╳ ╳     ╳ ╳ ╳
          │ │ │     │ │ │     │ │ │     │ │ │
        Leaf-1   Leaf-2   Leaf-3   …   Leaf-N
        (ToR)    (ToR)    (ToR)        (ToR)
          │        │        │              │
         Rack     Rack     Rack         Rack

Oversubscription: total leaf-to-server bw : total leaf-to-spine bw.

• 1:1 non-blocking (max performance, max cost)
• 3:1 typical compute
• 5:1+ acceptable for general workloads, not for storage

Step 2: Underlay Routing

BGP unnumbered (FRR / Cumulus / SONiC)   modern, no need to manage per-link IPs
OSPF                                     classic, simpler scale
ISIS                                     ISP-grade, used by hyperscalers

BGP-only DCs (Hyperscale pattern):

• Each leaf in its own ASN, each spine in its own ASN (or shared)
• ECMP across all uplinks (FRR / Arista EOS supports)
• Loopback IPs for router-id; underlay via /31 or unnumbered

Step 3: Overlay (if multi-tenant L2 needed)

EVPN/VXLAN
  L2 stretch over L3 underlay. Tenant separation via VNI.
  Type-2 MAC routes via BGP. Type-5 IP prefix routes for inter-VNI.

Use only if you NEED L2 stretch (legacy apps, vMotion, multi-AZ cluster requiring same subnet).
Modern apps prefer L3-everywhere.

Step 4: North-South — Multi-Homing + BGP

Get your own ASN + PI space for control. Multi-home to ≥ 2 transit + 1+ IX.

You (AS 65001)
   │           │
 Transit-A   Transit-B
 (Cogent)    (Lumen)
                      IX-1 (private peering: Cloudflare, Google, AWS, Meta)

eBGP to all 3. Outbound: LOCAL_PREF to prefer peering > transit (cheaper).
Inbound: AS-prepend for less-preferred ingress; MED only with same neighbor.

router bgp 65001
 bgp router-id 198.51.100.1
 neighbor 192.0.2.1 remote-as 174       ! Cogent
 neighbor 192.0.2.5 remote-as 3356      ! Lumen
 address-family ipv4 unicast
  network 198.51.100.0/24
  neighbor 192.0.2.1 prefix-list out-default out
  neighbor 192.0.2.1 route-map prefer-peer in
  neighbor 192.0.2.5 prefix-list out-default out

Step 5: Anycast

Same IP announced from multiple POPs. BGP withdraws on failure → traffic shifts in seconds. Use cases: DNS (root + recursive), Anycast HTTPS (CDN-style), Multi-region API gateway. Requirement: stateless or session-portable workload (anycast may hop mid-conn under churn).

Step 6: L2 Redundancy (within a rack/row)

MLAG / VPC   two switches act as one LACP partner
             servers LACP-bond two NICs to two switches
             survives one switch loss seamlessly
VRRP / HSRP  virtual IP shared by switch pair as default gateway
             sub-second failover

interface Vlan100
 ip address 10.10.0.2 255.255.255.0
 vrrp 1 ip 10.10.0.1
 vrrp 1 priority 110
 vrrp 1 preempt

Step 7: MTU + Jumbo Frames

1500   default Ethernet MTU
1380   safe for VPN encap (1500 - IPSec overhead)
9000   jumbo for storage / east-west (Ceph, iSCSI, NFS)
9216   modern jumbo limit (handles VXLAN + jumbo payload)

Rule: end-to-end consistency. One link at 1500 in a 9000 path = silent fragmentation / blackhole. Verify with ping -M do -s 8972 (don't-fragment).

Step 8: BGP Configuration — Arista EOS

! Arista EOS leaf switch BGP config
router bgp 65001
 router-id 10.0.0.1
 maximum-paths 4 ecmp 128
 neighbor SPINE-PEERS peer-group
 neighbor SPINE-PEERS remote-as 65000
 neighbor SPINE-PEERS bfd
 neighbor SPINE-PEERS timers 3 9
 neighbor SPINE-PEERS route-map FROM-SPINE in
 neighbor SPINE-PEERS route-map TO-SPINE out
 neighbor 10.0.1.0 peer-group SPINE-PEERS
 neighbor 10.0.1.1 peer-group SPINE-PEERS
 neighbor 10.0.1.2 peer-group SPINE-PEERS
 neighbor 10.0.1.3 peer-group SPINE-PEERS
 !
 address-family ipv4
  neighbor SPINE-PEERS activate
  network 10.0.0.1/32
  network 198.51.100.0/24
 !
 address-family evpn
  neighbor SPINE-PEERS activate
  advertise all-vni

Step 9: EVPN/VXLAN Configuration — Arista

! Configure VXLAN on leaf
interface Vxlan1
 description EVPN VXLAN overlay
 vxlan source-interface Loopback0
 vxlan udp-port 4789
 vxlan vlan 100 vni 10100
 vxlan vlan 200 vni 10200
 vxlan vlan 300 vni 10300
 vxlan learn-restrict-any-vni
 vxlan flood vtep 10.0.0.2
 vxlan flood vtep 10.0.0.3
 vxlan flood vtep 10.0.0.4

! EVPN address-family already under BGP
! Type-2 routes for MAC/IP advertisement
! Type-5 routes for IP prefix advertisement

Step 10: BGP Prefix Filtering

! RPKI-based prefix validation
route-map FROM-TRANSIT permit 10
 match rpki valid
 set local-preference 100
!
route-map FROM-TRANSIT permit 20
 match rpki not-found
 set local-preference 50
!
route-map FROM-TRANSIT deny 30
 match rpki invalid
!

! Prefix filter — only accept our prefix
ip prefix-list OUR-BLOCKS seq 5 permit 198.51.100.0/24
route-map TO-TRANSIT permit 10
 match ip address prefix-list OUR-BLOCKS

Step 11: EVPN Multi-Homing (Ethernet Segment)

! On leaf switches connected to same server
interface Ethernet3
 description Server-01 bond0
 switchport access vlan 100
 evpn ethernet-segment
  identifier 00:01:01:00:00:01:00:00:00:01
  df-election method preference
  df-election preference 150  ! higher priority leaf
  mpls bgp df-election include-pref-len
 lacp system-id 00:01:01:00:00:01
 spanning-tree portfast

Step 12: Carrier Diversity

Tier-1: ≥ 2 transit + ≥ 2 IX peering
Fiber entry: 2 physical entries to building (different geographic paths)
Conduit: separate conduits, ideally different sides of building
Provider: avoid two carriers riding same physical fiber underneath
Test: actual run from carrier maps; insist on diverse routes in SLA

Step 13: QoS and Traffic Shaping

Classify at edge:
  EF (46): VoIP, real-time       — strict priority, 5% BW
  AF41 (34): video, interactive   — guaranteed BW, 20%
  AF31 (26): critical data, DB    — guaranteed BW, 30%
  AF21 (18): standard web         — scavenger, 30%
  BE (0): best-effort             — remaining, 15%
  
Apply on all uplinks: shape, queue, police inbound to protect fabric.

Step 14: Network Automation — Ansible

# ansible/bgp-config.yaml
- name: Configure BGP on leaf switches
  hosts: leaf_switches
  gather_facts: no
  vars:
    leaf_asn: 65001
    spine_asn: 65000
  tasks:
  - name: Deploy BGP config
    arista.eos.eos_config:
      src: bgp-leaf.j2
      backup: yes
    notify: save config
  
  - name: Verify BGP neighbors
    arista.eos.eos_command:
      commands:
        - show bgp summary | json
    register: bgp_summary
    failed_when: bgp_summary.stdout[0].vrfs.default.peers | length < 4

  handlers:
  - name: save config
    arista.eos.eos_command:
      commands:
        - write memory

Step 15: Network Automation — Nornir

# nornir/bgp_check.py
from nornir import InitNornir
from nornir_netmiko import netmiko_send_command
from nornir_utils.plugins.functions import print_result

nr = InitNornir(config_file="config.yaml")

def check_bgp_peers(task):
    result = task.run(
        task=netmiko_send_command,
        command_string="show bgp summary",
        use_textfsm=True,
    )
    bgp_data = result[0].result
    peers_up = sum(1 for p in bgp_data if p.get('state') == 'Established')
    task.host["bgp_peers_up"] = peers_up
    if peers_up < 4:
        return f"WARNING: Only {peers_up} BGP peers established"

results = nr.run(task=check_bgp_peers)
print_result(results)

Step 16: DOCSIS / Fiber OLT Access (Last Mile)

For ISPs or edge POPs, apply cable access standards. DOCSIS 3.1 supports 10G down/1G up. GPON/XGS-PON for fiber to the home. Use BNG (Broadband Network Gateway) for subscriber management.

Step 17: Monitoring Tools and KPIs

BGP neighbor state          up/down + uptime + prefixes received
Interface counters          errors, drops, throughput per port
ECMP hash distribution      uneven = polarization, retune hash
Latency to upstream peers   ping / mtr from edge to {transit, peer}
DDoS / volume anomaly       netflow / sFlow / IPFIX export
Switch CPU/memory           control-plane load
Fabric utilization          per-spine / per-leaf link utilization
Optics DOM                  temperature, TX power, RX power, bias current

Tools: librenms, observium, Prometheus + snmp_exporter, flow collector (akvorado, pmacct), oxidized for config backup, batfish for config validation.

Anti-Patterns

Anti-Pattern 1: Single-Carrier Uplink

Full outage during carrier maintenance. Always multi-home to ≥ 2 transit providers. Use BGP with LOCAL_PREF to prefer primary, prepend AS for backup path.

Anti-Pattern 2: Mixing MTU Within a Path

One link at 1500 in a 9000 path causes silent fragmentation and blackhole connections. Verify end-to-end with ping -M do -s 8972. Document MTU per link in DCIM.

Anti-Pattern 3: No BGP Filtering

Accepting full BGP table from non-transit peers. Always deploy prefix lists inbound and outbound on every eBGP session. Use RPKI ROA validation to reject invalid prefixes.

Anti-Pattern 4: L2 Loop with STP

Spanning tree disables redundant links to prevent loops. Use MLAG/VPC for L2 redundancy instead. STP should only be a safety net, never the primary redundancy mechanism.

Anti-Pattern 5: Oversubscription > 5:1 on Storage Fabric

Storage traffic (Ceph, iSCSI, NFS) requires predictable throughput. Oversubscription above 5:1 creates contention. Design storage fabric at 1:1 or 3:1 maximum.

Anti-Pattern 6: Manual Config Only

Config drift, no audit trail, no rollback capability. All changes must go through NetOps automation (Ansible, Nornir, Salt). Enable config backup with oxidized.

Anti-Pattern 7: Flat Network (No L3 Segmentation)

Broadcast storms, large blast radius, no tenant isolation. Use VLANs or VXLAN for segmentation. Route at the leaf layer — never stretch L2 across the fabric unnecessarily.

Anti-Pattern 8: Single Fiber Entry into Building

Backhoe fade takes out entire site regardless of carrier diversity. Ensure two physical fiber entries from different geographic paths. Separate conduits and building entry points.

Anti-Pattern 9: Ignoring ECMP Polarization

Poor hash algorithms cause uneven flow distribution across ECMP paths. Use enhanced hashing (include L4 ports, entropy fields). Test with show ip load-sharing on Arista/Cisco.

Anti-Pattern 10: No BFD Configuration

BGP hold timers alone (30-120s) are too slow for modern DC failover. Always enable BFD for sub-second detection (3x 300ms = 900ms detect). Tune BGP timers to 3s keepalive, 9s hold as backup.

Production Considerations

High Availability

• Deploy BFD with 300ms interval for sub-second failure detection.
• Use Anycast for DNS, NTP, and stateless API gateways across POPs.
• MLAG/VPC + VRRP/HSRP for L2 device redundancy at ToR layer.
• Route reflectors at spine layer to avoid full iBGP mesh between leaves.
• Design for 50% headroom on spine uplinks during any single link failure.
• Quarterly fail-test: pull one uplink / one switch and verify auto-recovery.

Security

• RPKI ROA published for owned prefixes; RPKI validation inbound on all eBGP sessions.
• Prefix filters on every eBGP session (in AND out).
• Max-prefix limits on all neighbor sessions to prevent route table overflow.
• Control-plane policing (CoPP) to protect switch CPU from DoS.
• MACsec for intra-fabric encryption if required by compliance.
• Management VRF for out-of-band management access.

Performance

• ECMP across all leaf-spine uplinks; flow-hash tuned to avoid polarization.
• MTU 9216 in core, 1500 at edge, consistent within each domain.
• Use jumbo frames for storage and backup traffic (Ceph, iSCSI, NFS).
• Tune buffer allocation on spine switches for deep-buffered workloads.
• Monitor optics DOM for predictive failure detection.

Operational Excellence

• Color-code and label both ends of every fiber patch for ops clarity.
• Use digital optical monitoring (DOM) on all optics to predict failures.
• All changes via NetOps automation, never manual on prod.
• Separate underlay (loopbacks) from overlay (VNI) addressing plan.
• Run BGP timers aggressively: 3s keepalive, 9s hold for ToR-to-spine.
• NetFlow/sFlow export from every ToR for capacity planning + DDoS detection.

Security Considerations

Rules

• Multi-home BGP from day one for any north-south critical traffic.
• ECMP across all leaf-spine uplinks; flow-hash tuned to avoid polarization.
• MLAG/VPC + VRRP/HSRP for L2 device redundancy.
• MTU end-to-end consistent within a domain.
• RPKI ROA published for owned prefixes; RPKI validation inbound.
• Prefix filters on every eBGP session (in AND out).
• Carrier diversity: ≥ 2 physical fiber entries, different conduits.
• IPv6 dual-stack everywhere; IPv6-only acceptable for greenfield.
• All changes via NetOps automation, never manual on prod.
• Quarterly fail-test: pull one uplink / one switch and verify auto-recovery.
• Deploy QoS classification at edge; trust boundaries on all uplinks.
• NetFlow/sFlow export from every ToR for capacity planning + DDoS detection.

References

• references/bgp-anycast.md — BGP + Anycast — Policy, RPKI, Multi-Homing
• references/leaf-spine.md — Leaf-Spine — Clos Fabric, ECMP, EVPN/VXLAN
• references/network-infrastructure-advanced.md — Network Infrastructure Advanced Topics
• references/network-infrastructure-fundamentals.md — Network Infrastructure Fundamentals
• references/sd-wan-mpls.md — SD-WAN vs MPLS — Branch + Hybrid Connectivity
• references/vrrp-hsrp.md — L2 Redundancy — VRRP / HSRP / CARP / MLAG
• references/evpn-vxlan-deep-dive.md — EVPN/VXLAN Deep Dive
• references/bgp-automation.md — BGP Automation with Ansible

Handoff

• devops-datacenter for physical cabling and patch panels.
• devops-cdn-edge for global anycast and DDoS scrubbing.
• devops-cloud-architecture for cloud VPC and Transit Gateway alongside on-prem.
• enterprise-high-availability for app-level LB and failover.