---
title: Backend connection
summary: null
url: >-
  https://www.fastly.com/documentation/reference/vcl/variables/backend-connection
---

- [backend.{NAME}.connections_open](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/backend-connections-open/)
- [backend.{NAME}.connections_used](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/backend-connections-used/)
- [backend.{NAME}.healthy](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/backend-healthy/)
- [backend.conn.is_tls](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/backend-conn-is-tls/)
- [backend.conn.tls_protocol](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/backend-conn-tls-protocol/)
- [backend.socket.congestion_algorithm](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/backend-socket-congestion-algorithm/)
- [backend.socket.cwnd](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/backend-socket-cwnd/)
- [backend.socket.tcpi_advmss](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/backend-socket-tcpi-advmss/)
- [backend.socket.tcpi_bytes_acked](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/backend-socket-tcpi-bytes-acked/)
- [backend.socket.tcpi_bytes_received](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/backend-socket-tcpi-bytes-received/)
- [backend.socket.tcpi_data_segs_in](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/backend-socket-tcpi-data-segs-in/)
- [backend.socket.tcpi_data_segs_out](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/backend-socket-tcpi-data-segs-out/)
- [backend.socket.tcpi_delivery_rate](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/backend-socket-tcpi-delivery-rate/)
- [backend.socket.tcpi_delta_retrans](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/backend-socket-tcpi-delta-retrans/)
- [backend.socket.tcpi_last_data_sent](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/backend-socket-tcpi-last-data-sent/)
- [backend.socket.tcpi_max_pacing_rate](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/backend-socket-tcpi-max-pacing-rate/)
- [backend.socket.tcpi_min_rtt](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/backend-socket-tcpi-min-rtt/)
- [backend.socket.tcpi_notsent_bytes](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/backend-socket-tcpi-notsent-bytes/)
- [backend.socket.tcpi_pacing_rate](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/backend-socket-tcpi-pacing-rate/)
- [backend.socket.tcpi_pmtu](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/backend-socket-tcpi-pmtu/)
- [backend.socket.tcpi_rcv_mss](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/backend-socket-tcpi-rcv-mss/)
- [backend.socket.tcpi_rcv_rtt](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/backend-socket-tcpi-rcv-rtt/)
- [backend.socket.tcpi_rcv_space](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/backend-socket-tcpi-rcv-space/)
- [backend.socket.tcpi_rcv_ssthresh](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/backend-socket-tcpi-rcv-ssthresh/)
- [backend.socket.tcpi_reordering](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/backend-socket-tcpi-reordering/)
- [backend.socket.tcpi_rtt](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/backend-socket-tcpi-rtt/)
- [backend.socket.tcpi_rttvar](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/backend-socket-tcpi-rttvar/)
- [backend.socket.tcpi_segs_in](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/backend-socket-tcpi-segs-in/)
- [backend.socket.tcpi_segs_out](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/backend-socket-tcpi-segs-out/)
- [backend.socket.tcpi_snd_cwnd](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/backend-socket-tcpi-snd-cwnd/)
- [backend.socket.tcpi_snd_mss](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/backend-socket-tcpi-snd-mss/)
- [backend.socket.tcpi_snd_ssthresh](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/backend-socket-tcpi-snd-ssthresh/)
- [backend.socket.tcpi_total_retrans](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/backend-socket-tcpi-total-retrans/)
- [bereq.between_bytes_timeout](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/bereq-between-bytes-timeout/)
- [bereq.connect_timeout](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/bereq-connect-timeout/)
- [bereq.fetch_timeout](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/bereq-fetch-timeout/)
- [bereq.first_byte_timeout](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/bereq-first-byte-timeout/)
- [beresp.backend.alternate_ips](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/beresp-backend-alternate-ips/)
- [beresp.backend.ip](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/beresp-backend-ip/)
- [beresp.backend.port](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/beresp-backend-port/)
- [beresp.backend.requests](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/beresp-backend-requests/)
- [beresp.backend.src_ip](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/beresp-backend-src-ip/)
- [beresp.backend.src_port](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/beresp-backend-src-port/)
- [beresp.handshake_time_to_origin_ms](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/beresp-handshake-time-to-origin-ms/)
- [beresp.used_alternate_path_to_origin](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/beresp-used-alternate-path-to-origin/)
- [req.backend](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/req-backend/)
- [req.backend.healthy](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/req-backend-healthy/)
- [req.backend.is_origin](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/req-backend-is-origin/)
- [req.backend.is_shield](https://www.fastly.com/documentation/reference/vcl/variables/backend-connection/req-backend-is-shield/)