The remote server is having intermittent issues. Sometimes all three servers behind the host are gone, sometimes they block all packages.

# nmap -vv cyrus.andrew.cmu.edu
Starting Nmap 7.80 ( https://nmap.org ) at 2020-06-12 20:52 CEST
Warning: Hostname cyrus.andrew.cmu.edu resolves to 3 IPs. Using 128.2.157.16.
Initiating Ping Scan at 20:52
Scanning cyrus.andrew.cmu.edu (128.2.157.16) [4 ports]
Completed Ping Scan at 20:52, 0.13s elapsed (1 total hosts)
Initiating Parallel DNS resolution of 1 host. at 20:52
Completed Parallel DNS resolution of 1 host. at 20:52, 0.12s elapsed
Initiating SYN Stealth Scan at 20:52
Scanning cyrus.andrew.cmu.edu (128.2.157.16) [1000 ports]
Completed SYN Stealth Scan at 20:52, 2.88s elapsed (1000 total ports)
Nmap scan report for cyrus.andrew.cmu.edu (128.2.157.16)
Host is up, received reset ttl 239 (0.11s latency).
Other addresses for cyrus.andrew.cmu.edu (not scanned): 128.2.157.15 128.2.157.14
rDNS record for 128.2.157.16: CYRUS.ANDREW.CMU.EDU
Scanned at 2020-06-12 20:52:35 CEST for 3s
Not shown: 979 closed ports
Reason: 979 resets
PORT     STATE    SERVICE       REASON
23/tcp   filtered telnet        no-response
110/tcp  filtered pop3          no-response
135/tcp  filtered msrpc         no-response
139/tcp  filtered netbios-ssn   no-response
143/tcp  filtered imap          no-response
445/tcp  filtered microsoft-ds  no-response
515/tcp  filtered printer       no-response
631/tcp  filtered ipp           no-response
993/tcp  filtered imaps         no-response
995/tcp  filtered pop3s         no-response
1433/tcp filtered ms-sql-s      no-response
2000/tcp filtered cisco-sccp    no-response
2003/tcp filtered finger        no-response
2967/tcp filtered symantec-av   no-response
3389/tcp filtered ms-wbt-server no-response
5555/tcp filtered freeciv       no-response
5900/tcp filtered vnc           no-response
5901/tcp filtered vnc-1         no-response
5902/tcp filtered vnc-2         no-response
5903/tcp filtered vnc-3         no-response
9100/tcp filtered jetdirect     no-response

Read data files from: /usr/bin/../share/nmap
Nmap done: 1 IP address (1 host up) scanned in 3.42 seconds
           Raw packets sent: 1025 (45.076KB) | Rcvd: 980 (39.200KB)

# nmap -vv 128.2.157.16 128.2.157.14 128.2.157.15
Starting Nmap 7.80 ( https://nmap.org ) at 2020-06-12 20:54 CEST
Initiating Ping Scan at 20:54
Scanning 3 hosts [4 ports/host]
Completed Ping Scan at 20:55, 5.03s elapsed (3 total hosts)
Nmap scan report for 128.2.157.16 [host down, received no-response]
Nmap scan report for 128.2.157.14 [host down, received no-response]
Nmap scan report for 128.2.157.15 [host down, received no-response]
Read data files from: /usr/bin/../share/nmap
Nmap done: 3 IP addresses (0 hosts up) scanned in 5.10 seconds
           Raw packets sent: 24 (912B) | Rcvd: 0 (0B)